Rounded off hex headed screws

[RobW]

Just tried to undo one of the screws on the underside of the chassis on my Losi 22 and I've managed to round off the screw head (2mm hex type).

Any top tips out there on how to remove it?

My last resort would be to dremel a slot in the head and then use a flat headed screwdriver to remove it but given I've already proven myself to be a bit hamfisted today I am concerned I'll end up cutting a groove in the chassis as well

Anyone else have their own favourite method?

Thanks in advance

Rob