I don’t need to use Cubase on the 2 computers, only the recording one.
It seems that the only solution is to invest 20€ in another USB e-licencer and then move Halion and Groove Agent to this new e-licenser.
Buying another Halion and Groove Agent 5 license could be avoided because I don’t need them when registering so I can run pure Cubase with its SE versions.
The VST waltz 
Not perfect.
One last question : what if I connect the 2 USB e-licenser on the same computer ? Are we limited to one USB e-licenser by computer ?