Mudkipz

Hi Could someone tell me how to make an archway intersection, similar to what is shown on the vaulting junctions tutorial, but instead of having a 4 way junction, I want a T-intersection between two vaulted corridors. In dromed, it was as easy as making two cylinder brushes intersect, but for some reason I cant seem to find a nice way to do this (with brushes) on dark radiant. Although my main interest is to know how to pull this off with only brushes, I'd really appreciate if someone told me an efficient method to do this with patches. Thanks