Don't really see any way to control the TiVo with no remote.
But -- I have a really nice universal remote by X10 I bought for home automation that also works well with my TiVo (ALMOST all functions work but haven't figured out the advance / commercial skip button equivalent yet.)
For what you want to do, would work fine and REALLY cheap right now as they are blowing the out in anticipation of whatever is replacing it: only $4.99 at http://www.x10.com/promotions/ur73a_ed_499.html?EM#
(.. and no, I'm not getting any cut from that link. You can also go to the x10.com site, then click the SALE link and scroll WAY down to near the bottom if you'd rather.)
You might also just check around with friends and neighbors to see if anyone has an old universal remote they don't want anymore that they'll donate, and then look online for the manuals (since it's doubtful they'll still have them) to get the code for TiVo. But not likely the X10 remotes are going to last long at that price.
(I'm buying a few more just for the convenience of not having to take it from room to room and then look for it :-)