Hi,
I am not sure if many people here have started using that service.
Sounds like you may need to set it up as a ProxyVM similar to the way people setup a TorVM (
https://www.qubes-os.org/doc/torvm/). This would be the location in which you would install the I2P software to enable the appropriate network access.
You probably then need to setup a separate AppVM that is configured to us the proxyVM. This is where your browser or other software would be configured to use the ProxyVM to access the I2P network.
This is just my interpretation of what may be required but I have not tested.
If you do work something out, it would be good if you can share for people in the future to have a starting point that has been tested.
Regards,
Iestyn Best