You might find it easier to fit them on the VGA pins on the board itself, a lot easier than surgery on your vga cable or getting inside the monitor itself....
For the short length of cable used it won't really matter that the 75ohm resistors are fitted on the cga-vga card. (on the VGA connector of course).
Otherwise, the other way would be to grab a small vga/dongle casing (as used on the CGA side of things), and fit the resistors in there.

Good luck, hope it all works out 100% and it should be a good fix to spread around to everyone who needs it ;-)

Tried it out this morning, but due to not having the the 75 ohm 5% resistor (They did not have any & told me this would be better? maybe full of shit!?)
I had to get the 75 ohm 1%... I don't know if this is why it is not working but I soldered and earthed it and the is no difference at all

Here is a picture of the 75 ohm soldered to the vga end, grey dongle side is the cga