I need a lateral thought

You can set up a "dummy" machine (w. internet access) that makes the work transfers, then stop the client there, transfer the whole BOINC directory to the other machine, let the work collected crunch there, then transfer the BOINC directory back to the internet machine, start the client there and update the projects to report the results and get new work.

The exact procedure depends on the OS. With some clients there is also a way to manually start a benchmark run, so the powerful machine wouldn't have to live with the presumingly poorer benchmark results from the dummy one.

If the internet machine will crunch BOINC by itself, you can set up the "dummy" as a VMWare virtual machine, on Linux it will be enough to use a different "BOINC" directory, on Windows it might be best to install another BOINC client as a different user and into a different directory than the default one (Program FilesBOINC).

BM