Here's one option you could try. This drawing may help in explaining the theory of the hydraulics behind it.
(This is an abbreviated drawing of just the chaeto section of my sump.)
The total sump flow enters the right side chamber. Inside the right side chamber is a pump (the bigger the better, well, within reason of course. No need to flow more than your total sump flow.). Coming out of the pump the flow is teed off

angry-face:? No, not as in mad, just split

), then comes through the right side baffle and shot into the main chaeto chamber through eductors (spreading them out to each side helps to center the chaeto ball within the main chamber). In the above drawing, the blue line represents the flow that the pump itself creates. Because the pump is in a separate chamber, the intake does not get clogged. This flow gets pumped into the main chamber and then flows right back out over the left baffle. That flow by itself would tend to draw the chaeto over the left baffle. This is where the eductors come into play. The green line represents the additional flow that is picked up by the eductors. Because the source of the green flow is picked up within the main chamber, it just circulates within the chamber creating a horizontal vortex. This helps keep the chaeto in a spinning ball and off the walls and bottom. The red line represents the additional total flow of the sump (at least in my case) and allows for a water level equilibrium between the right and main chambers. If the pump you would use has a flow rate higher than the total sump flow, the slot at the bottom of the right baffle would allow the water from the main chamber to return to the right chamber. Blah blah blah.... sorry if that was a little on the long winded side, hope you're still awake.

Now in all honesty, does that keep every little loose strand of chaeto balled up. Not quite, but close. That's why I also have a piece of large open pore cell foam running across the opening of the left baffle. It catches a few loose pieces making it easy to remove instead of going to the return pump. This will happen more when the chaeto ball gets huge but that just means it's time to harvest!
As I said, this is just to help explain the theory. Implementing it into your sump will be up to you if you choose to try it.
Hope this is of help to you.