OK, you have a three way switch feeding the ceiling outlet. First step is to go take that outlet out of the ceiling and see if you have a 14/3 feeding it. (If you do, you'll have a red wire in the box.) If you do, great! You (probably) won't need to pull a new wire.
Now, the next step is to figure out where [which switch] that box is fed from. If it's fed from where you want the control, you're golden. If you have a red in the box, it's probably in the middle of the circuit and to make this work, you'll end up stranding one of the switches as useless. If it's fed from the side that you don't want to use for control, you can still do it, but you want to physically take the feeding switch out of the circuit and make both red and black from that switch always hot, then feed the black to the always hot outlet and the red out to the switch you want to maintain and take the black return from that switch to run the outlet for the lights. Easier to open up the box, figure out what you have, and we can help you from there if you can't draw it out yourself. (It seems like you have a pretty good handle on the situation, so you should be good.)
That will allow you to split feed an outlet (red switched to one outlet, black always hot to the other outlet for the garage opener) and also to take that red feed out of the box to run the other hard-wired lights. You could also run the always-hot to both receptacles in the box and run the red switched to the lights. Your call.
If the garage door outlet is at the end of the run and fed from a 14/2 (no red wire in the box), you're going to have to go with something like your plan. What Whiskeymike and I were suggesting was to use the GDO as the light switch and run your lights off of that. (IOW, instead of using X10, use the GDO. Many have a way to lock the lights on.) All the lights would come on when using the GDO, of course. That would be trivially easy.
Another choice would be to use the GDO to switch a solid state or a mechanical relay if you're concerned about the current flowing through the garage door opener's relay. (I wouldn't hesitate to run 120W of LED lighting off that relay, since the GDO was probably designed to run 2 60W incandescent lamps anyway.)