Multibate is a derivative from 'multitask' and 'masterbate' in which a busy person on the go may not have time to 'masterbate' as they have no time to fit this into thier already hectic schedule. So they perform both tasks at the same time. Thus resorting to multibating.
Buisness man john is at work furiously trying to create a report on the financial risks of spread betting. As the tension gets to him he figures he needs to relieve himself then and there. So he 'multibates' at his desk i.e masterbating while writing his report.