Ok, I REALLY wanted to not have that extra RF remote sitting around just to run the TV lift and was determined to make this work.
This is my story.
Step 1: Buy extra TV Lift remote from the company that sells it. It was remarkably cheap. $15, and they even paid for the shipping.
Step 2: Buy electronics kit that can use IR to close a relay. (Velleman MK161) I originally thought this kit could use any IR code, but it can't. You need to also buy the 2-button remote control (Velleman MK162). These kits are just parts and need to be soldered together, but it's through-hole soldering and not too tough.
Step 3: Assemble this stuff, and then take apart the remote and wire the relays to the button contacts on the remote. Basically, when the relay closes, I'm effectively 'pushing' the button on the remote (make sure MK161 is set to close relays only momentarily rather than toggle them off and on).
Unbelieveably, this thing actually worked. All I had to do now was make it nice. I bought a project box, and some little nylon stand offs from Fry's, then ordered the required power supply from DigiKey (and instead of just using the bare wires, I decided to also get a couple of jacks so I could just plug it in). I also picked up some IR window plastic so I could make the box look nice.
Step 4: Set to putting all of this stuff together. (Note, I was able to ditch the battery for the remote, since it was the same voltage as the power supply and required by the MK161. I just wired them up in parallel.
Step 5: Drill a hole in the box for the power supply jack and cut another hole in the front for the IR window (Dremel is handy here). Then you just use the standoffs to stack the boards a bit (I'm a bit of a hack, so I just glued them down).
Step 6: Add the MK162 remote to my Harmony. I made a new device, called it an 'Appliance' and set the two buttons as discrete on and off signals. Then just tell the Harmony software that you want the 'Appliance' on in every activity, and when you start up it will send the 'on' (up) signal, and lift the TV.
All Assembled, it's just a black box with a power supply jack in the back. Plug it in and basically make sure it has IR line of sight to your remote. Done.
Believe it or not, this thing basically works like a charm. Been running it for about a month now with no problems.
Just wanted to share in case other people have similar problems.