A few points:

1) Whenever your itinerary includes any non-upgradeable flights (in your case, HEL-FRA), United will just ignore the upgrade request for the whole itinerary and show the lowest fares. Pretty poor functionality but that's how it works.

2) You can call to get a D/C fare. Some D fares may not be refundable and be substantially cheaper than full C, and there is just no way to force .bomb to offer them in your situation.

3) You can upgrade LH flights with SWUs on a standby basis (for this you have to call MP and have them convert the SWU to paper for LH use). The hit rate for upgrades to first is high, and you can upgrade Z fares. The upgrade is not confirmed so it's a bit of a gamble, but you have a chance to access the FCT in FRA, and F service (if not seats) is much superior to UA. In the worst case, you fly LH C which is competitive with UA F unless you get the new UA seats.