Mobat- in your tank, I would try this: get another, square piece of clear acrylic, large enough to hold the side-mounted filter, and some large suction cups. Drill a hole in each corner of the acrylic, to attach the suction cups to the acrylic. Use the suction cups to attach this acrylic to the back or side of your tank (on the inside) and mount the hanging filter on that piece of acrylic. You will have to mess about with the sizes and etc to make it all work, but I hope this makes it somewhat clear.
This way you can use a side-mounted hanging filter in your tank.
