Need a way for a parent to sign a waiver for a minor for an unmanned facility when only teen wants to play

Right now, it appears the only way is through public booking. I wanted to distribute the kiosk guest waiver to some high schoolers before a 17 year old birthday party but have no way for their parents to sign.  They legally cannot sign for themselves and since they drive their parents will not be present. This is an unmanned facility with remote access.