OK, now it's a bit clearer, you have and need to use the 6-speed wheel as a stop gap, right. OK, you could just install it as is in the frame and squeeze down on the qr or nuts to compress the frame, sort of cold setting in reverse.
Better would be to respace the 6-speed wheel to 130 mm by adding 4 mm worth od spacer(s) to the non-drive side, recentering the axle and redishing the rim.