I must agree with cavok_flyer! Dealing with the German Aviation Authority LBA can be a pain! Additionally if your initial EASA Medical was issued by a German AMC (Aero Medical Center) you will encounter major issues when it comes to transferring your license to another EASA country, since the LBA won't release your data due to the German data protection law (see link at the below). Not to mention the "Zuverlässigkeistprüfung" (reliability-check) as already stated above by cavok_flyer, which is kind of a personal background check conducted by the Germany authorities every few years. If there is a little discrepancy (e.g. you forgot to pay a ticket a few years ago) you pilot license might be suspended, not a good thing for a commercial pilot! In Germany and any other EASA member state there is no such thing like a "stand alone distance learning course" you must attend some additional ground school in order to be allowed to take the exams! To my knowledge, there is only one school in Switzerland which provides a "stand alone distance learning course" without attending any ground school for ICAO CPL/IR holders (I provided the link below). Alternatively one can attend a full time ground school course, there are a few schools out there providing full time courses, like Bournemouth CFT or CATS. Do you have EU-citizenship or the legal right to work in the EU, otherwise it would be pointless doing the conversion?! Anyway good luck!
http://www.pprune.org/medical-health...SA+Medical+LBA
Ground School - Bournemouth Commercial Flight Training (full time course)
https://www.catsaviation.com/courses/atpl-fulltime (full time course)
https://www.bristol.gs/ (distance learning -very good reputation)
Special Conversion Offer Courses - Horizon SFA (Switzerland - no ground school required)