My quick notes. I'm running an Eberron campaign with Pathfinder Beta rules. I frequently pull beasties from the SRD without doing much to change them. All you have to keep in mind is the CMB, some feat changes, and the skills.
Skills can be done on the fly as:
If the monster is good at it: 3+HD+Ability bonus
If the monster isn't good at it: Ability bonus
It isn't perfect, but it works pretty well on the fly.
I know the final rules will include additional changes, like the Combat Maneuver Defense, but that looks easy enough to figure on the fly also...HD+Str+Dex+10.