If you already own the manifolds, you have several options. Buy a brass "Close nipple" Something like this
. (I'm not sure that's the right size, I just used 1/8" as an example)
Or you can replace the cap on one of them with another MFL-NPT nipple, and use a piece of hose.
Or you can spend the cash on a dual regulator, and run 2 pressures.
If you don't already own the manifolds, I'd just get one that has the number of ports you're looking for. $40.00 for a 5 port at CHI Company