The first one you mentioned - is that under ERRORLOGFILE in that registry folder?
I would create a parameters one as well. We had this problem recently and that resolved it. Obviously, back up the registtry etc. if this is production. It should be under parameters, then SQLArgX, where X = the number it is in the startup parameters, i.e. if it is top of the list, then SQLArg0, if it is second, then SQLArg1 etc.etc. I cant believe they dont exist as that is where the info in the startup params come from. Worst case, search the registry for SQLArg and see where it lies.
Cheers,
M.