When I was flight instructing, we often did not make students pay for the .2 or .3 involved in run-up and taxiing back to MX. My rule was if you didn't pay, you don't log.

Personally, I don't think it's really loggable, and it does look suspicious if you did. Think about it, 0 takeoffs, 0 landings, .5 TT? It really isn't worth it.