As of this moment, the industry is making a liar out of me. A few years ago,
Waterway® made a real nice in line filter that had like 1" or 3/4" fittings on each end that would work directly with a circ pump like this. It was about the size of an oil can.
I guess the market didn't support it and it's not in their catalog anymore. Tell you what though, we're direct Waterway distributors on the east coast, and I'll have the boss (Babe) check on this thing tomorrow and post again... to see if there's any left over, or if there's a suitable option for you.
Thanks for reminding me about this.
PS: Waterway® deals with so much stuff, including things like 2" and 5" speaker systems for hot tubs... lol, now I'm waiting for the next volcano jet sub-woofer. Your requirement for this kind of accessory isn't unique. It's the plague of anyone with trees around the tub!