Don't go calling or emailing Doepfer right away,
but if DIY-ing is not your thing you might find this next thing interesting:
" In principle Doepfer is able to make special designs, but most customers underestimate the time and consequently the costs for a special design.
Normally there are three steps for a custom design:
Development of the hardware (provided that none of their existing hardware products can be used), development of the software (provided that the design includes a microcontroller) and design of the mechanics (e.g. controls, housing, provided that the customers is not able to built his own case).
The hardware and software design is carried out at Doepfer, i.e. design of the schematics, PCB layout and software.
All mechanical parts of the design - i.e. PCB manufacturing, housing, treatement of the housing like drilling holes, milling slits, varnishing, printing and so on - is carried out by other companies specialized in such things.
Doepfer has no mechanical working place in their company.
The main problem for a special design is that all nonrecurring costs - i.e. design of schematics, pcb layout, programming the software, initial charges for the pcb manufacture, case/housing production and silk-screen printing - have to be payed by one customer only.
Even for a small design these nonrecurring costs reach the few thousands Euro range.
Normally these charges are divided by the number of devices that are manufactured (a few hundred or thousands as a rule).
Please keep in mind all these notes if you ask for a special design.
If you are willing to pay for all these steps of work they might make a quotation for you. "
from the Doepfer FAQ page