The installer can be run with a /s switch to install silently, but it's going to prompt on first run to start the trial period or to unlock your registered purchase.
The activation system is somewhat liberal, but if you are constantly redeploying fresh images and reactivating essentially a new VM each time, you're going to have trouble eventually. A far cleaner solution is to install Start8 in the base VM, activate it, and then use that as the core of the snapshot/image your are deploying. If you are using multiple licenses/running copies, purchasing some additional ones would also be appreciated.
That said... the following could be called from a script to activate a registered copy without interacting with the UI. From the application directory:
SDActivate.exe -silent -appabrv=st8 -email=your@email.com -password=password -sigpath="C:\ProgramData\Stardock\Registrations\start8sig2267.bin"
Kris