Here is the call to bollinger bands from the manual:
Code:
BBands(vars Data, int TimePeriod, var NbDevUp, var NbDevDn, int MAType)

The return values are stored in: rRealUpperBand, rRealLowerBand, rRealMiddleBand.

Call BBands and subtract rRealLowerBand from rRealUpperBand and viola, bollinger band width.

Cheers,
BobbyT