Unfortunately there is no way to copy banks of sounds around on the REV2 itself, but it could be easily done using a computer editor...
Since the bank you bought is in bank2, you could ask the seller, if they can provide the SysEx file in four versions (one for each bank)... alternatively I can set up a file for you, but that would have to be the Prophet-8 bank from DSI that I can split into two SysEx files where the first 128 sounds are in bank1, and the next 128 sounds in bank 3 (so that they do not interfere with bank2 that your bought bank will load into).