Use a rag wash, stipple or scumble with a sponge or even a mop. 

Seeing your using studio flats, grab a board & test paint it. You may wish to do it with an organic movement, of scollops or the like, to set up a patten. Or as a goush with the mop, then scumble or stupple with a complementry or contrasting colour, dependant on the period required?
Doing a test sampler, might  save a lot of messing about!

I love the textured rollers too. I taped off squares for stones over the base coat, used the roller, removed the tape, then shaded in the stones. One castle interior  done in an afternoon.

I have used the textured roller a couple of times. after KathyS suggested it a while ago, they are great!
especialy rather than walpapering flats, which I hate on sets, but that's my hang up.
Using various methods of scumbling, stippling or mop/rag washing & getting the whole cast & crew involved, is the best fun you can have with buckets of paint. Also they all feel that much more involved & get a sence of ownership of thier creation. Of course there will always be those Luvvies & Twirlies who will be so delicate they have to wear covering for protect the skin softness of their hands & other bits, especialy the blokes. But if you use water based plastic [latex] paint, just advise them that it will protect as well as any rubber gloves.
You could pick up those protective paper coveralls, bonets & booties, from one of those 'Work Safe' shops or procure from a friendly industrail work site.
They are cheap enough & your artists will be less inhibated & may bring out thier artistic bent? Hiccup is they can be  a drama when they want go to the dunny? Also very revealing if they become too wet.
I feel you will get a more free form artistic effect.