There is an Airbus approved procedure in FCOM 3 for single engine taxi prior to departure.
At bmi we have been doing this for quite sometime now and don't seem to be having any problems with it. All the normal engine warm up times apply so no problems with taking off with a cold engine, you just need to manage it (or not bother doing it in the first place) if you have been shut down for 2 hours of more. Officially there is no limitation on weight but my experience is that at high weights on the 321 you struggle.
There are various tech. and weather criteria that must be satisfied and also extra procedures for after start and engine start phases and these are all contained in a different coloured "normal" checklist that we use from before start to take-off if we have decided to do a s/e taxi out.
All works well most of the time, just occasionally someone (not me of course!) gets the timing wrong and isn't ready to line up when cleared but its pretty rare and the procedure can easily save 100kg of fuel on a 09R day at LHR so its well worth doing in the right circumstances.