Something I used to do before I got myself that 6x12 roll film back was to cut one sheet film shade in two halves. So I take such a half along (the one with the grip). When shooting panoramas I compose the panorama to be either the upper or the lower half of the sheet film / ground glass. When exposing I remove the standard shade and insert the cut/half shade either at the top or bottom of the holder. If I position the panorama at the top, I place the half shade at the bottom and vice versa. I expose, then remove the half shade and reinsert the full one.
This way you can get two panoramas on one sheet. Although it won't be 6x12, more like 5x12. Cheap solution, will just need to "sacrifice" one shade.