[NTG-context] Font features for \ss only?

Hi all, how would I make sure that \ss always uses one set of font features while \rm always uses the default feature set? Do I need to specify this in the typescript file? The reason is I'm using Myriad as \ss font and would like to enable the capital spacing (cpsp) OpenType feature for that while activating a different feature set for all \rm instances (Minion in this case)… Many thanks, Oliver