Thank you both for your help!

@Pilou
It's a nice feature on which I have to take a closer look, however I didn't help me in the case of specifying the exact length without going manually again to the d-field.

@Michael
The problem I have with the Edit-size Menu is that even if I uncheck 'Maintain Proportions' and use 1D scaling, it scales the object equally to both sides. And for my usecase it's important that I can select the starting point, endpoint and then have the exact length typed in.

Thing is, the workflow I've shown in my post works perfectly fine, however, it's just a bit tedious to have this back and forth between keyboard & mouse.
I found a script here: http://moi3d.com/forum/index.php?webtag=MOI&msg=10769.2 which lets me open up the Edit-size Menu by using a shortcut. Question is now, would that also be possible for the d-Field?

Thanks again!