Thickening Too Thin Chocolate

I've recently started using a different supplier for my white couverture (Agostoni).When the chocolate is in temper, the viscosity is too thin to coat enrobed items (especially weak on outside corners). I've used a touch of additional heat & cocoa butter to thin down overly viscous chocolate before, but have not encountered the opposite problem.

Does anyone have any suggestions for how to thicken overly viscous white chocolate? Will the addition of more milk powder do it? Anyone with experience?

Thanks!