I had it happen on my '05 Sprinter. The "fix" is ugly as home-made sin but it works.
You have to cut a hole in the grill, left of the center and near the top of the grill, to admit your hand and a pair of Channel-lock pliers. Reach your hand up in there and feel the latch, there are a couple of extensions that you'll feel. One is the anchor point for the cable housing-- it doesn't move--, the other is the movable part of the latch. Put your Channel Lock on this so it bridges these two points, then squeeze. The hood will open.
After that, you have a choice to make. Either buy a new cable and a new grill, or-- leave it be, and just get used to the new way of opening your hood.
Note: I learned of this when I had a broken cable by looking at a Sprinter parked next to mine at the warehouse I was working at one morning. He was doing something like checking his oil or something, so I took a real good look at the latch mechanism and saw exactly how it worked and what it was like underneath where you have to reach up with the tool. If you can find a similar model year Sprinter- it doesn't have to be exactly the same year, these things don't change much from year to year--it pays to have a look, get a "feel" for exactly what you're reaching for, and have a go at it. In any case, the job will have to be done through the grill, and since the grill could only be removed after you had the hood open you'll just have to cut a hole in it.
I hit the jackpot here-- it shows what you're reaching for. Look at the picture below. On the left side of the latch, where the cable connects, see the two extensions. One is the fixed point the cable housing mounts to, the other is the moving part the cable core connects to. You'll have to feel for it from underneath, but-- that's what you're looking for.
