If you like DIY projects, you can make an acrylic hanger for your heater, intake/output pipes and possibly powerheads.
I made my first hanger using a clear acrylic wreath hanger cut to size. I have since just used narrow strips of acrylic cut from a large sheet and use a heat gun to warm the acrylic so it can be bent into a hook that hangs on the rim of the aquarium.
Here is a completed heater holder using the stock Eheim holder minus the suction cups.
I removed the suction cups and drilled the posts to accept #4 x 1/2" long stainless steel pan head phillips screws.
Measure the distance from the top of the hook to where you want the heater mounted on the acrylic holder and drill holes through the hanger, using the heater holder to mark the spots.
This is a very simple project to do and I have used it for both holding heaters and canister intake/output piping. I have not tried it for powerheads because they usually aren't mounted on the rear of the aquarium.
If you use glass canopies or hoods, you will be limited on where you can place the acrylic holder because it needs to hang on the rim of the aquarium.