Excuse my poor drawing skills, but would it work with the stepper sideways? It'd need the usual spring loading on the skate bearing, but this minimizes load on the stepper shaft. The J-head (in this case) has a mounting slot which could align with a plate (like the Mk.7). With a bit of thermal paste this would couple it to the carriage and allow it to act as a heat sink. For PLA it'd also need a little fan under the carriage pointed into the J-head cooling slots. I must work on this!
Hmm. I think it's about time I learnt Sketchup, or got a proper CAD tool.