i've used 22 ga wire for extensions up to 18 inches in length and haven't had any issues so far, i use heat shrink tubing over each wire and then another piece over all three - this helps with the issues of the joint flexing and becoming unstable.

also, should you go the solder route....i suggest plenty of practice on scrap wire before you tackle the acutal joint. i've been an electrician/machinist/maintenance worker for 15+ years and i still make at least one practice joint before i solder the actual joint together (i guess old habits die hard) LOL