Hi,

is it possible to install a Hipshot D-Tuner on the E-String(!) of a 5-String Bass? (Musicman Stingray 5 HH)

pOgO

If it is strung EADGC, why not? :D
Just joking, the best way is to ask Jason from Hipshotproducts.com, he is a very helpful guy. Or you can do what I did:
Find the Xtender model that will fit your Bongo (I don't know if there is a direct replacement one), download a picture, scale the picture to 1:1 (I mean measure for example the distance between the two screw holes, have print out and scale it making it bigger or smaller accordingly). Put this 1:1 scaled picture in your bass and check if it will fit. But my senses tell that the arm of Xtender will probably touch the tuner of B string when you drop E.

The Hyper part comes from the fact that it uses 4 detuners for an array of alternate tuning possibilities.
Although it is a 2 on a side 4 string which makes for a little exta room.
http://www.zonguitars.com/zonguitars/hyperbassspecs.html

AFAIK they are no longer making the Hipshots with Levers to reach around another peg. In this case, the answer would be no.