Once you have the tivo set to alternate addresses, then you need a universal remote with enough learning memory to be taught commands from both tivos. Or a universal with preset codes for alternate addresses, and the philips models in the first link have codes for address 1 & 2.

Older models from One-For-All like the urc-8820, urc-10820, urc-6820, and urc-6690 have preset codes for 4 tivo addresses. If you go after those older OFA model, beforewarned that OFA replaced the 8820 & 10820 with the 8820N & 10820N, which do not have these tivo alternate address codes.

Do you have universal now, if so was is the brand and model #?