I would get one of your 7-pin connectors, wire to something like this:
Adapter 4 Pole to 7 Pole Vehicle End Trailer Connector Tow Ready Wiring 30717

Then use the tow ready bulb out adapter

Then get the opposite connectors and make a reducer cable to get back to your 7-pin flat.

If you didn't want all that loose, you could get a small electrical box and have a pigtail out that goes to your vehicle with the 7-pin flat, has all the adapters plugged in and a pigtail out with the final 7-pin flat. Then mount the box to the trailer, similar to how I do with the RF unit.

I couldn't find anything that converts the US round plugs to yours, but you can buy the connectors.

__________________
Daily Drivers:
- 2008 535i, 320,000km
- 2004 X5 4.4, 01/2004 production, 420,000km
- 1997 328i, 350,000km

Track:
- 1996 328i, track/race car, ~300,000km

Winter:
- 2013 Ski-Doo MXZ X 800 E-TEC, trail can
- 2007 Ski-Doo MXZ Blizzard 800 HO
- 2001 Ski-Doo MXZ 600 w/800 engine, exhaust
- 1978 Ski-Doo Olympique 340 (vintage race sled)
- 1977 Ski-Doo Olympique 340E