Well as it turned out my pronto codes above didn't work. Not sure why but I suspect that it has to do with not knowing the carrier frequency of the IR. I tried codes for both 38kHz and 40kHz and neither worked.

However, following advice from Screen Innovations, I was finally able to get the URC remote to learn in the original remote. Here's how we did it -

1) Activate learn mode on the URC software.

2) Place the remotes "eye to eye", but place your hand between the two remotes.

3) Press and hold the button on the original remote that you wish to learn in.

4) While holding the button, remove your hand from between the two remotes.

5) Once you see the "Learn OK" message in the URC software, release the button on the original remote.

6) If you do not get the "Learn OK" indication upon performing these steps, adjust the remote positioning and repeat steps 1-5.

Once we performed these steps (and we did have to do some buttons 2 or 3 times before we got the "Learn OK" indication), the URC remote successfully learned in the original remote.