Yes, a short 30mm dia. wooden dowel, glued into the bottom of the seatpost would increase the length of the seatpost, just enough to fit the CrossRack and still lock the fold. I measured my Brompton seatpost's I.D and its 30mm. I.D=Inside Diameter.

Another plus to the CrossRack is it also fits the Xootr Scooter...i often use the scooter for short 1-2 mile runs to get groceries....i hang grocery bags off the handlebars...it works OK, but you have to slow down, or the bags swing too much...the CrossRack should work much better and can be instantly swapped to any of my 3 bikes which is a major plus to me.