I wouldn't bother, I think it's a prerequisite of working as a dispatcher that you have to be a fat, lazy, pot bellied, tattooed, disinterested, idle Scouse git. I'm sure it's somewhere in the small print on the Servisair website anyway
Seriously, I guess it wouldn't do any harm, but I sure as sh!t wouldn't delay the FI rating thing for the sake of being a dispatcher ... 50 hours instructing will look better on your CV than 50 years of dispatching that's for sure.