Cursitor Doom wrote
Anyone come up with a solution to the problem of making voltage readings
on high impedance parts of a circuit with a meter of a different Zin to
that used by the people who wrote the service manual?

If it is available look a the circuit under test, and see if the high impedance
does make a real difference.

Else use the scope probe... Do not some of them modern Di Gital makes also display volts?
If meter impdance is too high and no other way add a resistor in parallel to your meter?