take a piece of filter pad and put it over return...
in a pinch use teflon tape to thicken up the end, if needed. then secure the pad with twist ties. but change the pads every few days.
asci illustration...
== is the teflon
| is the twist ties
_|_______
[hr]
==- }
[hr]
==- }
_|_______}
if the bubbles are real bad, get a filter pad that's a pouch and fill it with some bioballs, it will help disperse the bubbles.