An update.
I have a bit of a droopy finger that won't straighten fully - this is expected for this sort of injury. The tendon is longer than it used to be.
The long period of splint and cast use has caused arthritis in the proximal joint (1st one from the knuckle). I need to do about 15-20mins exercises when I wake up as it is basically swollen and rigid first thing in the morning, although that can be helped if bind the joint a bit overnight. A little bit of pressure stops the swelling. Anti-inflammatories help too. I do other 5 minute exercise sessions every couple of hours through the day as well.
The therapists have been brilliant, wanting to understand the movements of a bass playing finger and figuring out how to assist. One of the exercises is to have a flat bit of paper on a table and put the hand on it flat and then pull all the fingers in to crumple it - sliding the fingers on the table. That is remarkably similar to plucking a string while using a ramp, drawing a finger along a flat surface with a string just being in the way.
So I raised a flat topped pickup on my Sandberg to act as a ramp and it is letting me play far better than I have been recently. I have more control and just as importantly it's preventing my finger from hooking too much and stopping the fingernail catching on the string. I can now play as therapy as well.
2 of my basses have flat topped EMG pickups so they will get raised to be ramps. I've bought some epoxy for the others following Billy Sheehan's old method of covering exposed pole pieces with it and then sanding to shape them.
I've been videoing some of my playing - close up right hand - so I can see what I'm doing more easily and adapt a bit. It seems that if I rotate my hand leftwards a little, so the string contact is closer to the left side of the finger rather than the middle of the finger pad, the movement restriction is less of an issue, particularly when the tempo is a bit higher.
Also the therapists have come up with a strapping system that gives a bit more control in strengthening the finger while trying to straighten the tip, and that won't get in the way of playing. I can play at home without it, but I can strap it for gigs / rehearsals where I'm likely to play harder.
The overall position now is that I can play the stuff my big band plays - not as well as I used to yet, but very close. The Billy Sheehan type stuff is a long way off, but I don't play that sort of thing very often anymore as I've become old and boring!
Rehearsals start on the 18th Sept. Be interesting to see how it goes.