If you have taught a que word try using that! thats what we did, as we wanted to train her to only wee and poo on grass not pavements etc (and not our patio!!)
We used exactly the same method of saying 'do a wee, or do a poo' and then rewarding her as we did in the garden. Worked really well and its suprisingly useful to be able to get her to wee and poo on demand!