The golf rod of the lock is really small and fiddly yeah... if you've got big hands you're gnna find it slightly more difficult than usual lol..
The boot doesnt use a rod at all, as far as I can remember there's a plate on the outside of the mechanism which is dark grey/black. This is solid and moves freely attached to the lock itself, so something I thought about doing was drilling a small hole in this plate, putting some sort of pin through the hole and attaching the solenoid in the same way you do normal locks, but instead of connecting to the door fiddly rod connect to the pin you've put in there.. (tell me if that doesnt make sense). Screw the mechano-looking piece in the usual way and you should be on your way...
I'm not priviledged enough to own a gti

So i'm afraid I'm gnna be unable to help with the petrol cap!
GavGti - if you look in like the second or third posts you'll see an ebay link or 2, 1 of them is for a remote upgrade kit, that's the kind of thing you need..