Executing a PROC from a DATA Step, Quentin commented and drew my attention to a highly informative SAS Global Forum paper on the same subject by Mike Rhoads. I'm grateful to Quentin; Mike's paper offers a lot of insight and experience in this subject area.
Mike's paper is entitled Use the Full Power of SAS in Your Function-Style Macros and it describes how you can run a DATA step or a PROC within a user-written function which, in turn, can be called from within a macro statement. Mike describes the catchily-named Macro Function Sandwich technique, and provides a number of illustrations of how the Base and Macro languages can be extended with this capability.
I'm hoping to see even more papers on this subject area at this year's SAS Global Forum. I think it offers a lot on untapped potential.