So, intrigued by your problem, and being an old pre-press person, I took a look at ya problem, and lo and behold, got it to work on my stoneage non-postscript HP Deskjet 840C, but it's a PITA, I must warn you!
1. In the print configuration dialog (From Print & Fax -> setup printers), choose add to add a new printer.
2. You'll see the dialog box presenting you with protocol types and other stuff. I assume your printer is a USB printer and then you'll be presented with a box with your printer model already in it, in the case of USB. Select it and choose a printer model with the Epson Stylus Photo 1280 CUPS - GIMP. Click ok to all of that.
3. Now add another printer. This time choose IP Printing with the LPD/LPR option. type localhost into the location box, some name without spaces into the name box and choose a generic postscript printer from the model list. Click ok to all of that.
4. Go to illustrator and in the page setup choose that latest generic postscript printer with the name you gave it in the previous step. Voila, the separations menu item becomes enabled.
5. Select the separations menu item, and then choose the PPD option. Go to your Illustrator folder in Applications and look in the sub directories for a folder called sample PPDs. I chose the Generic one, but you could just as well choose the other one for Distiller. Click ok to that and set up your separation. click ok to that too.
6. Now select print and and in the Illustrator part of the drop down options select color separations and set your choices.
7. Now go to Output options and select save as file. Select Postscript in the drop down list.
8. Click save and save it somewhere.
9. There are now 2 ways to get this puppy out: The first is to start up your GIMP-CUPS EPSON printer from the print center and drag your .ps file onto the printer in the dock. The second is to double click that .ps file and wait until it opens in preview (with separations!) and then print that. Your choice. I tried the former and it took a while but worked just fine.
10. I was able to print full color pages to my old HP with no problem from Illustrator using the HP driver (not the GIMP one) According to EPSON's website, the driver for your printer is included in OSX. You can try the GIMP-CUPS version but the results will probably not be as good, although they will at least give a decent LPI.
Hope that gets your ball rolling.
(That'll be $200 for a late support call please

)