After lots of trial and error, and a little inspiration from Koji, I have written a new script that will run when you select "update snapshot" in the yellow ! button on any MEDM screen.
Right now, it's only live for the OAF_OVERVIEW screen. View snapshot and view prev snapshot also work.
Next on the list is to make a script that will create the yellow buttons for each screen, so I don't have to type millions of things in by hand.
The script lives in: /cvs/cds/rtcds/caltech/c1/scripts/MEDMsnapshots, and it's called....wait for it....... "updatesnap".