If you have complicated ABAP to write, why not get an ABAP programmer to write it? It's my view (and experience as an ABAP programmer in the BW environement) that there's a huge amount of inefficient and badly written code in BW implementations! For example, it's good practice to remove the ABAP code out of the routine, so that within the routine there's merely a call to a class method (or function module).
Since you have already got programming experience, why not go on BC400 or buy one of the many "teach yourself ABAP" books?