Can I Connect RGBW LED Strips With LAN Cable?
Past few weeks I have really come to appreciate the benefits of cable pull string. A nylon string used to help pull cables. You can drill the holes in the walls, cover them up and then when you get your cable, tie and tape it on one end, then pull from the other. Just make sure you make the holes big enough to pass the flat ribbon RGBW cable through along with the knots.

If you don't have cable pull string, you can get it at most hardware stores and the big box stores. You can also just use any strong string or twine you have. If you have UTP cable you can put that in temporarily then use it as a pull cord but it's not as strong as the pull string. That shouldn't be a problem for a small run like you're describing if it doesn't have a lot of sharp bends.

The problem with running UTP is that it's normally 24 gauge and even though it might just be a temporary fix, temporary can sometimes be a very long time as long as everything appears to be working and you have other things to do. So it's thinner than the usually 22 gauge RGBW cable conductors. According to this table on wire properties 22 gauge wire can handle up to 0.92 amps for power transmission and 24 gauge wire only 0.577 amps. If you know how many amps your light setup will use then you can make a safe decision.

When you have to use a different wire it's better to go with a larger size than a smaller size. You can get 5 conductor thermostat wire most places and that's generally 18 gauge. 18 gauge wire can handle up to 2.9 amps for power transmission so it's the safer choice.

I would personally just make the holes, pass some string, leaving plenty on each end to tie and grab, then install the cable when you get it.