Stridsberg sells a power injector.
It is called a "Bias T". They offer different connectors for it and you supply the power adapter that has the correct voltage rating for your amp.
You may need to redo the tip of the power supply so it plugs into whatever the bias T has for a power jack. I thionk they will also sell opne with a solder post feedthru cap for your power supply leads.
They may be a bit more than you were expecting though. Try googling for a bias T. They are a very simple circuit that you could build easily.
The Amp is a Scientific Atlanta single port.......As far as me building it...........YEA RIGHT !
I think somewhere someplace a court order is in place banning me from doing and electrical type work....lol