Hi, the mitten looks great
When you say out of working yarn do you mean you have no yarn left? or the working yarn isn't connected to anything?
If you do have yarn left then what I would do is start first with the dpn with 2 stitchs, pick up 2 sts with your yarn right before the dpn in that gap, then work the 2 sts on the dpn, so now you have 4sts on each dpn. You just continue knitting until you are ready for the decreases.
You can make the cuffs fit more snug by casting on less and then increasing when you reach the hand, dropping a needle size, or you may try making the cuff longer so it can be tucked into a coat.
Amy has a video on picking up sts on this page,
just scroll down