In the original RM2 "Spell Law", there's no modifier for the absence of verbal component: it's not a mandatory element (chapter 10.9 doesn't mention it). However, the "Spell User's Companion" refine what component is actually needed: verbum, motus, symbum, gemynd, and gredus. According to that, what the absence of one component does is an option, and left to the GM. In your case, one suggestion would be to increase the cost of the spell (in PP), or to give a penalty to the BAR or the EAR.