This sounds to me like the classic "Volumetric CBC" approach: show multiple products on the screen and ask respondents to allocate purchase volume to the concepts (where the purchase volume is not held constant per task).
MBC software will not do this. It requires a bit of customized analysis beyond CBC. You may use our CBC software to design, field, and collect such volumetric CBC data.
But, the analysis of the Volumetric CBC data is not automatically supported by our CBC software. You need to do some extra stuff on the back end. There are two models that I can remember off the top of my head that are sometimes done by our users:
1. "None picks up the slack" approach. This is the easier method and is described at: http://www.sawtoothsoftware.com/help/issues/ssiweb/online_help/hid_web_volumetriccbc.htm
2. Two-step logit + regression approach (trickier than option 1). See Tom Eagle's 2010 Sawtooth Software Conference paper at: http://www.sawtoothsoftware.com/support/technical-papers/conference-proceedings/proceedings2010