Discover sequential segmentation: Analyse behaviour prior to a visit/event

The sequential segmentation in discover is really useful.  However, I want to be able use the functionality to isolate what happened "pre" (or post) some significant event/action.

An obvious use case would be to look at what users do in visits prior to a purchase (1 visit prior, everything in the 30 days prior etc).  In order to do this I'd need to exclude the visit in which the purchase occured and all subsequent visits.

The issue with the current functionality is that the sequence has to sit in a visitor container. So I can define a segement that looks at visitors who had a visit prior to a  purchase visit, but this results in everything that the visitor has done being returned - not just what happened prior to the purchase event.