I'm not sure what role the screen plays in the metering system on the EF, but if it plays no role, you could get a custom solution, like a Maxwell screen, but it wouldn't be worth the cost--might as well just sell the EF and buy a later Canon with a better screen like a New F-1 or T-90.
Later Canons, however, have a prism in the screen that diverts some of the light to the meter, and there are no aftermarket replacements for these, and they aren't easily swapped between cameras. This, incidentally, is why later manual focus Canons need a circular polarizer rather than a standard polarizer, because the meter won't work properly with the regular polarizer.