You should still be able to fit the original fender with the dual disc set up.
My bike's at the other end of the country atm but from what i remember, the mounting brackets from the fender are different either side, one has a kinda bump in it that goes around the outside of the calliper mounting arm hinge point, while the other is just flat. The mounting bosses on your forks should be slightly different either side so that to fit the second calliper you mount it with the flat bracket of the fender between the fork and the calliper mounting arm.
Mine seems to work fine with this arrangment, sorry if the description is a bit iffy.