I initially thought otherwise, but after looking at the REG, I must agree with Prof:
Play As: Unused enhancements may be placed here face up during Discard Phase. Holder may return one enhancement from Storehouse to hand during Preparation Phase. • Identifiers: Holds any number of enhancement cards.
So, this is now another card that might be impacted by the fortress ruling. If the ability to take them out is negated, is there any way to get them out other than say, Spreading Mildew?