Hello Cavebear,
May be it's a good idéa, but i newer saw an old frame MARTIN like this system, i don't know if you can drill the beam ?
I think it's more easy to put an additional tank.
Ask to EGLI, he know lot about EGLI and MARTIN frame.
In this pics you see a new frame that Georges MARTIN sail now he have like Egli frame a tank for oil in the beam.