In our company it is acceptable for an engineer to 'sign in' the a/c provided that the outgoing Captain (or FO if Captain is uncontactable) is able to confirm maintenance status and inbound fuel remaining. Failing that, we are able to use inbound flight paperwork to confirm required details, and tanks can be dipped as a confirmation that fuel readings are indeed correct.
I'm surprised you have no procedure in your company Ops manual.