At the moment there is no feature in Net::Appliance::Session to do the equivalent of send_wakeup.
If you are comfortable patching the code yourself, I'll tell you what (I think) needs to be done:
Take a look at the Serial transport (Serial.pm) and you'll see it does a wake-up (look for "wake the serial connection up"). Copy this code into the Telnet or SSH transport module after the fhopen and it'll do what you want.
Sadly of course this isn't something you can easily turn on and off. However I do see the value in this feature, so I'll add it to my TODO list for sure. I am planning to put a lot of work into improvements in the module in the next month.
I hope that helps,