Hi Ben, thanks so much! Your reply inspired the following approach. It may not be the most optimized processing but I think it will do the job!
Create new field on contact record for Split Value
Create 5 update rules to set Split Value to A, B, C, D, or E (I need 5 random, even groups)
Create Program that uses percentage based routing to route 20% of full contact population to each update rule
Set each of 5 rules in Dynamic Content item to Split Value = A,B,C,D, or E
By the way, we're using this to drop into emails a blurb prompting recipient to add job function to their profile if missing in Eloqua. We have 5 different ways of saying this and want to use all 5 for awhile dynamically to test which messaging works best.