Thanks gents.
Wayner: Not so much perspiration in this case……………..more eye strain

A quick update after some further exploits.
The cactus tool turns out to be pretty much ideal for carefully prising out pieces of embedded dirt.
I ended up using a fine grade wet 'n' dry paper (dry) to sharpen up the tip a little and it works a treat.
The good thing about the cactus thorn is if I accidently jump sideways it doesn't appear to damage the grooves, well at least so far so good on this front.
Probably just not quite hard enough to cause too much damage when used carefully.
But for trying to tidy up scratches it's not really up to the task, not being stiff enough to dislodge the deformed vinyl.
I can subtly improve the level of the click but am not able to noticeably reduce it.
The sanded down thorn I used from a domestic house cactus deflects just too easily and is not able to scrub the damaged plastic aside.
So it's left me in a bit of a quandary as what to try next?
As Douger mentioned, it does look as though some form of razor blade or as I mentioned in my OP a scalpel/craft knife is required.
The problem with this is I'm really not sure I can hold one of these (with a suitable handle) steady enough to chase a groove without hopping over a couple of grooves and risking making things worse.
I suppose if the scratch is bad enough not to play the disc there's not much to lose.
Probably a bit more trialling of the technique might help a little.
Am certainly going to continue to use the rig and cactus tool for locating and fixing pops, but need to mull over what's best for trying to fix scratches.
I do like the idea of a scalpel/craft knife, but it needs to be small enough to fit between the lens and the disc - no more than 3/8" high.
Grafting part of a razor blade onto a similar wooden carrier is probably the way to go with this – thanks Douger.
I should be able to form this into just the right shape for the job.
If anyone's got any other thoughts - I'm all ears.
Cheers
Dave