That's not going to work, as such. You can't exactly "amplify" CVs or modulation signals and arrive at a useful result most of the time. What you can do, though, is to use an adder to add a DC offset voltage of a given amount to raise the CV/mod level. But the sort of amplification you're talking about here would probably be pretty useless...and potentially destructive, as an x2 'amplification" of a 10V p2p modulation signal would give you a 20V p2p one, and that's apt to damage circuits that're used to seeing no more than 10V or so at their inputs.
Have a look at the Doepfer A-185-2, vpme.de's T43, or Tiptop's MISO...all of which are useful for modifying CV/mod levels. But the thing that I'm wondering here is that, if Eurorack and the Roland System 100 use the same CV/gate standard, why do the levels need boosting from the Eurorack to the Roland system? Everything should track 1:1 between those two.