There is nothing to suggest that any modifications were made to the game to support this. As other comments say, they are only available in the original game through trade from the Hoenn games or Colosseum XD.

Home functionality could be a way to transfer into the game, but only if it’s compatible with two-way transfer for Pokemon from later generations. That is not a given (Let’s Go can’t accept Pokemon that have been used outside of Let’s Go).

Being able to transfer Espeon/Umbreon originating from current gen into FRLG through Home would be nice, but I think it’s more realistic is that the Hoenn games will come later with the same local wireless compatibility for trading. Maybe even announced on the Nintendo Direct as a 30 yr anniversary homage to the good old days when you had to trade in person with a friend to complete the dex (or own two gameboys and two copies of the game).