You can purchase an external oil pump which is actually the pressure stage of a multi-stage dry-sump pump.
Back in the early 90's, before I went dry-sump on my historic race car I used a gilmer drive pulley to drive an external pressure pump that pulled oil out of the sump, and then sent it thru the cooler and filter and back into the engine.
I'll search the web for a reference and update this page a bit later.
See an example here:
http://www.vpw.com.au/Category/Index/6169
and a picture of the general arrangement on a 60's Mopar 6-cyl engine here:
http://i165.photobucket.com/albums/u...er23809053.jpg
Picture taken from a thread on this forum ... link ...
http://www.queenslandchryslers.com/f...php?f=9&t=1301