It can be done, because I've done it. But I'll be dipped if I can remember what I did...
Even though I can't find them right now, I'm pretty sure that there was another little plastic chip that snapped into the bottom of the remote, and it had a setting for IR. However, it's entirely possible that the 612 didn't come with that chip, and I used the one from my 722 to do the programming.
If you don't have a chip for the IR setting, you might still have a chance. If you remove the existing chip, you will see that there is a tab with a V notch cut in it. That notch moves a small slide switch in the remote to one of several positions, which changes its mode.
If you remove the chip, you can reach in with a small probe, and gently slide the switch to the various positions. Try the operation at each position and see if one works for you. That's pretty much what I did recently when I tried to get the 612 to recognize both an IR and RF remote simultaneously. I'm not sure how I did it, but once I got the status screen to show IR/RF remote (instead of just IR or RF) it worked. I can now use the universal IR remote in the main viewing room with the HD TV, and use the RF in a remote room to view SD over the RF output. (Of course, the same thing has to be playing on both TVs, as the 612 doesn't have a second independent TV output.)
Good luck, I wish I had the definitive answer for you, other than to say keep trying, it can be done!