The mounting bolts for Shimano dual pivot brake calipers are available in different lengths. The only difference between the front calipers and the rear calipers is the length of the mounting bolt. Moving the front caliper to the rear is a way to get a dual pivot caliper onto the rear wheel.

To get a dual pivot brake calipers onto the front wheel, what about doing some reach into the part number of the mounting bolts and finding one that would be long enough to swap with the one that came on the rear brake caliper (since you are using the front caliper on the rear wheel?).

I already have some mounting bolts leftover some when I did some changes on my bile and had to get longer mounting bolts for the dual pivot calipers. If I remember correctly the original mounting bolts were a touch too short for my taste, so I had my LBS order some longer ones for me.