Axle length relative to drop-out spacing is rather critical, installing a couple of extra lock nuts will certainly increase the OLND (over lock nut dimension) but will compromise safety by reducing the axle stubs. You need a few mm within the drop-out lest the back wheel drop out. With solid/nutted axles there is usually enough to play with but on QR axles just adding spacers is asking for trouble.
Much more proffeshnal to cold-set the rear triangle to suit the new hub, its easy to do (depending on the strength of the frame) just remember to align the drop-outs and hanger properly afterwards.