The Carenado Piper Seneca II comes with a minipanel that displays the most important instruments on a narrow black strip but that is much more easy to read than the virtual cockpit.

 

A very important instrument I am missing there -and there is plenty of space- for IFR operations is the DME. When doing IFR (and why not VFR) it is very useful to have the DME instrument in the minipanel to easily see the current distance to the VOR reported by the DME instrument. The DME on the VC is not so easy to read and since it is on the side to read it one must deflect the view angle and zoom in, thus loosing attention from the main thing: flying.

 

How can I add the DME (which AFAIK is the standard Bendix DME from stock FSX) to the minipanel?

I don't own the plane, but the method is the same for all. You have to locate the correct panel.cfg in the SimObjects\Airplanes folder. Find it under the aircraft's name and then go into the panel subfolder. You'll find a file called panel.cfg. Make a backup.

 

Now opening the file with e.g. notepad shows you the entries, one of them being the popup for the instruments. So you see a list like this (this is from another plane!).

[Window Titles]
Window00=MiniPanel
Window01=GPS
Window02=Toggle_AP
Window03=Toggle_Manual
Window04=Toggle_Control
Window05=INFO

Lets say your popup is the Window00=MiniPanel and you want to add the DME to it.

 

Well, you now have to scroll down a bit to see Window00 being defined. Sizes, gauges, placement. You'll add another gauge, so you need some extra spacing and should make sure to place it below, above or beside the other gauges. So you don't lose information.

 

As for the gauge, you can grab some default FSX one. Bendix_King_Radio!Bendix-King Radio DME sounds good, so place it as the next gauge in line. Mind the numbers! With a bit of testing, you may find a nice layout serving your needs and since you've taken a backup of the original panel.cfg, you can always go back.