This technique currently has no practical use in a speed run that completes the game.
The only time the game performs a check to see if Link has the Flippers in his inventory is when he physically enters or jumps into a body of water; it does not continuously check for them as a condition to remain swimming. It follows then that Link can swim without Flippers if he can find an alternative means to start swimming than directly entering the water. While that may sound all-encompassing, indirect mechanics do exist within the game that place Link in water, already swimming, without bothering to check for Flippers in his inventory.
A respawn location is always maintained by the game so that it knows where to place Link in the event that he falls into a void, lava, or water (without Flippers, i.e. drowning). If this location is itself submerged in water (or just slightly above it), then upon respawn the game will just place Link in a swimming state. It will skip the inventory check to verify that Link has the Flippers on the assumption that the respawn location could only be in water if he already had them. That is to say, manipulating the respawn position into pointing to a submerged location and then having Link respawn there will activate Fake Flippers.
Screen transitions that divide bodies of water can be used to manipulate Link's respawn location. When Link hits a screen transition, the game will automatically set the respawn location to exactly where Link first enters the next screen following his short walking animation. This is set regardless of how high/low Link is above/below the ground and no criteria is used to prevent this from being set to potentially "undersirable" locations. Therefore, getting Link to hit a screen transition just slightly above water will cause him to transition to the next screen, drown, and respawn with Fake Flippers activated.
Getting Link into the correct position to activate this technique is performed by dashing diagonally off of ledges (gotten onto via Damage Boosting) into water heading towards a screen transition. Link's starting position for this is somewhat precise, although not believed to be pixel-perfect. The following table shows valid setup positions Link can dash from to successfully activate Fake Flippers:
|North-East of Turtle Rock||Requires Damage Boosting onto ledge. Allows entry to Turtle Rock without Flippers.|
|East of Turtle Rock||Requires Damage Boosting onto ledge. Allows entry to Turtle Rock without Flippers.|
|Path to Witch's House||Requires Damage Boosting onto ledge. Odd invisible wall around bottom left-most part of ledge must be maneuvered around to get into position.|
|Near the Letter in a Bottle||Requires Damage Boosting onto ledge.|
|Area North of Dark Palace||Requires circumventing the auto-jump barrier by using a bomb to knock Link into the screen transition as he jumps.|
The most important aspect of the setup positions is Link's distance from the screen transition, which directly affects the trick's success (or lack-there-of):
The behavior observed when Link is too close to the screen transition makes this a very dangerous trick to attempt in speed runs. If you are unsure of the setup position you are using, always err on the side of being too far away rather than too close.
The alternative Rising Water Method mentioned below has the added benefit of automatically setting the respawn location to Link's submerged location after the water has risen, meaning that Link can reactivate Fake Flippers for free if he exits the water but only walks on land that doesn't update the respawn location (such as rafts).
If Link raises the water such that the location he's standing in becomes submerged, Fake Flippers will automatically activate.
The Flippers Treasure Dungeon is the only location where this method can currently be used. In theory, it should also work in a few rooms in the Swamp Palace, however this cannot be verified as those rooms cannot be reached without the Flippers themselves.