The original prototype of the Shadow SH-950 used an acoustic guitar strap knob jack (1/8” jack inside, 1/4” jack outside) inside a transparent PVC tube together with a releaseable cable binder. Might have been too expensive for series manufacturing but works well and you can quickly remove the pickup with or without the jack. Just a bit more weight on the tailpiece.
Compared to the Underwood the pickup elements of the SH-950 are indeed a bit thick.
The cable can get stressed at the jack and at the pickup elements. (Had that both and was able to resolder at both positions.)
Be very slow and check often when the elements get in with some more force only, the difference to “barely holds without falling out” which delivers the best sound is very small, like a very soft fine file stroke.