I've seen people use these with some success - just tucked around the pickup tube. I have not tried my self and don't know how in the hell you would clean it afterward:
(Stainless Steel Scour Pad - in case the pic is gone at some point)
That, or just use a hop sock/sack. There's a few people on here that have rigged up paint straining bags to PVC collars to rest on the lip of the keggle.