The plastic pieces from the World Chess Academy set are compatible with the DGT Pegasus without any modifications needed.
I tried today out of curiosity and they're recognized by the board just as easily as the DGT Pegasus pieces. They function just as well during gameplay with no wrong moves and no glitches.
To be fair, the board feels a bit crowded in the beginning but it's worth it, since the bigger pieces are easier to pick up and more ergonomic.
If you happen to have both, it's worth trying it out if you haven'f already.