Don't do it man! 5212's are definitely not worth it... maybe 5360's.... but don't take your life for a handful of 5212's.
easiest thing I do to upgrade the sip f/w (I assume you're in sip mode), is switch to minet mode, point them at a teleworker server (MBG) using the '7' key to program mbg's ip address, let them boot up and they will download the latest version of all the files... the sip and minet code is in the same file, so you just switch back to sip mode after you are done.
oh look, an MBG running latest s/w is at 216.191.234.111...
I've never used the sip config files, I just http into the sets and muck around directly.