We have had the same problem.
The issue with adjusting the bolt on the end of the cylinder is that it only puts pressure on the spring. If the piston has bottomed out at the end of the cylinder, no amount of adjusting the bolt will do any good.
You are right, your pads have worn to the point where there is no adjustment left.
Amel have pads, but neither of thew two Maud showed me were like our pads, which seem to have quite a bit of material still on them.
So, what to do?
I took off the cylinder and caliper assembly, disassembled the floating caliper and drilled a 7mm hole through it where it contracts the piston pin, threaded the hole M8 and put in a bolt with a lock nut, so now I can adjust the distance between the caliper and the piston pin.Put it all back together and adjust the bolt so that the shaft can't spin, test with engine on that it is able to turn....
That's fixed it.
Elyse SM437 Levuka, Fiji