Yes you can. All you need to purchase is the G2 valve. The internal kettle dip tube parts are all interchangeable. When you remove the G1 valve you will also remove the o-ring and o-ring retainer. These are not needed with the G2 valve, it comes with an o-ring face seal.
You can work with our local Blichmann retailer to order the G2 valve.
You can also purchase one on the Blichmann Engineering Replacement Parts site at the link below.