I had exactly the same problem with my SMP 300m GMT... exacerbated by the fact that I have palendromic rheumatism which has left me with with very little strength in my hands.
Here is my solution to the problem:
OK - a miniature g-clamp would work just as well as my tool-makers clamp. You just need to attach something that will allow you to get a good grip on the srewdriver, so that it doesn't slip and bugger the slot in the screw.
It makes sense to take a sharpening stone to your screwdiver first, in order to ensure that it is a good fit in the screw.
Tthis cheat enabled me to shift the threadlocked screws in my Omega SMP - despite my rheumatism.