Ogres really seem your best bet, and I would really say that even if your green stuff skills aren;t amazing, cloaks/coats can be accomplished fairly easily.
I'm going to point you at the coat I did for this Eldar guy as an example.
All you have to do is press the green stuff down flat, then cut out a shape and lay it over the models back. Do thin strips down the sixes, and the once dry smooth the gaps between the pieces with green stuff.
Its easy to do.
Of course your other option is to remember the concept of scale.
40k is about 1/48, so something in 1/32 would be about the right size.