An identical remote to the TV2 remote, which was a UHF Pro 6.0, will work and is probably the cheapest. Newer remotes will also work, but they'll be more pricey. The UHF Pro 6.0 remotes have a 2-position switch under the TV1/TV2 tab, and the remote is rather simple in that the switch makes it IR-only, or UHF-only. That is how both TV1 and TV2 remote addresses can be set to channel 1. The receiver knows that it's TV1 if it's IR, and that it's TV2 if it's UHF.
What I did was buy another UHF Pro 6.0 for a few bucks, flipped the switch over to TV2 to turn the UHF on, and then I took the tab out and carved on the plastic such that it can't move the switch to IR any longer. Reinserted so that it said TV1.

Then I went to the System Info screen (with the IR remote I still had) and got ready to set the receiver TV1 channel to IR + UHF channel 2. I know, that's a little confusing, but it takes fewer steps to make TV1 use channel 2 than it does to make TV2 use channel 2. Ah... Then you follow the instructions in the manual which I don't recall very well. But IIRC you hold down the SAT button until it starts blinking, hit the numeric key of the channel you want (such as 2), and the pound sign. This sets the remote to UHF channel 2. Then hit the Record button, and this should change the receiver TV1 to your newly hacked UHF remote.