Nathan, did you consider the option to put your flash off-camera? TTL flash cables are very cheap today-I got mine from ebay for 20 euros or so (it is just some wires put together after all....)
i use the 550 ex with the EOS50 and works nice, very nice-with some effort I can illuminate objects nicely even beyond 1:1
I could use my macro setup with the EOS5 (film), but actually the EOS50 (a recent buy) has a better TTL flash metering (E-TTL instead of A-TTL) and the transparencies come out just exquisite!
and you can still play around with some small light reflectors