Somebody wrote this and it sounds like a damn good idea:
Just a little trick I learned back in the Nam:
A couple of years ago I was trying to pre-prime an engine prior to break in. It was about this time of year and the garage was probably 10 degrees F. I had the priming distributor chucked up in a 1/2 Milwaukee Hole Shooter and it was a struggle to even hold the drill motor - never mind get oil flow up to the rockers.
I took a couple of contractor flood lights, set them on milk crates so they were right up near the oil pan, turned them on and walked away for the night.
Next AM - still just as cold in the garage. But when I cranked up the drill - what a difference! I could hold the drill handle with one hand, the gauge I had screwed into the top oil port immediately shot up to 45 psi and oil was gushing out of the tops of the push rods within a minute.
Since then I always use heat lamps or flood lights (even in warm weather) to pre-heat the oil in the sump (it usually gets up to about 120 F). I figure that way, it is getting to every far corner of the system - much more effectively than if the oil is cold.