Why don't you have a barrel made that has an integral 1/4 rib and scope bases? Although not a single shot, take a look at the integral EAW mount machined into the rear square bridge of the Johannsen Mauser 98 actions www.johannsen-jagd.de . It may also be possible to have an integral front pivot base.

As Sinner mentioned above, if you don't want any protrusions on the rib when when the scope is removed, then the rib could be machined with ruger style "slots" which would enable the use of a number of different rings, such as Leupold's. However, the scope may not automatically return to zero when re-mounted.

Why don't you talk to Martini and Hagn? They will advise on integral options for single shot barrels.