How about disguising the heater.....like this....
HEATER COVER - 002
DETAILS Rocks designed specifically to hide heaters and cords, a fantastic way to finish off the natural appeal of your tank. MEASUREMENTS [product_additionwww.universalrocks.com
Those are good. I made a similar thing for a 29g using a long chunk of bogwood (Malaysian Driftwood). You want a good current so the filter return next to it works.