Anybody have some clever solutions to isolating the LE5-series MF from the cabinet?

The JBL cabinets used a dense cardboard tube end, stuffed with batting, with the MF leads caulked through the tube wall.

There's four problems in trying to approximate this, near as I can tell:
- must acoustically isolate the MF
- must be firmly attached to the baffle
- must be minimally sized to minimize the impact on cabinet volume
- must be mounted so as to not interfere with the T-nuts.

How have you'se guys beat this? What have you used?

A 5-inch PVC end-cap would be divine, but I haven't seem any.

Thanks!