Selecting tab in tab control sets Type: can it be done?

I have edited the Mini Window Edit Appointment layout, so that the tab control includes the following tabs: "Encounter", "Call", Tox Screen", "Other." These correspond to my four appointment types (Encounter, Call, Tox Screen, Other.) Now, I'd like to set things up so that when the user selects a given tab, the resulting appointment is set to the corresponding appointment type. I've fooled around a little, trying to insert a Type field radio button array underneath the tab titles, but can't seem to get that to work. Can you suggest a solution? Thanks again for all your help with this!