It "should" be reasonably painless, depending a few things.

You will need the Protozoa expansion card for the Proteus to make this happen.

The Protozoa card has the first 128 presets from the P1, P2 and P3. Then, a fourth bank of "new" presets.

You should install the card, then copy the P2 bank to RAM bank "0". This will place those 128 presets in the first 128 locations.

Now the tricky part:

If the Proteus 2 used stock sounds, in their original locations you should be good to go.
If you moved or edited sounds, you'll need to move and/or edit sounds into the same locations as his P2.

Hopefully your P2 is still up and running so you can A/B the two units. You'll need to edit the new sounds on the card to match his older edited sounds and then
save them to the same preset locations he had saved them to on his P2.

Now, if all the presets and the locations match, you'll be fine.