I found out that DT Swiss spokes and DT Swiss 12mm nipples have about 1.25mm of spoke sticking out from the nipple head.

I will first try to find nipples which allow greater protrusion ( others say they get about 2mm of spoke sticking out but those were only estimates )

I believe the 12mm nipples should work according to the calculations. If not, I will try the washers.

M4 Spring Washers.

I got Mavic Open pro rims which seem to have strong double eyelets. So I don't think having washers between the nipples and the eyelets will effect the integrity of the wheel.

dabac, I think I will bring the nipple and the rim if I do plan on getting washers.