If this was my bike, I would plug bike charger into wall outlet assuming the LPR mode is still recognized when bike wakes up.
To wake up bike applying 9V to the VCU side of the fused circuit, placing power supply 0V to AC charger gnd, do not feed the battery pack side...use a bench power supply w/ current limit set to 100mA or try it w/ a fresh 9V battery or maybe two in parallel which is self limiting to ~200mA below the 315mA fuse size.
If there's enough residual charge in the battery pack, the DC/DC converter should fire-up which means LPR is recognized if it glitches and shuts down quickly then an additional isolated 12V supply is needed because pack is way depleted and for that you will need a connector adapter to isolate 12V - again, I would not backfeed into battery pack and mind proper circuit polarity with respect to AC charger gnd and you'll do fine to not harm anything further...we can source parts to make adapter your bike is newer than mine but the following should carry over in terms of identifying the pack connector and the keep alive fuse...

There's only (2) circular connectors on the older bike, one for battery pack interface and one for charger interface.
For comparison, looks like Energica went to rectangular connectors for the newer Eva series, the following is preliminary...

Sanity check w/ dealer first to be certain and HTF does one activate the friggen spell checker in our replies?