This is going to sound a bit odd, but try putting something underneath the centre of the long axis of page so the paper has a slight curve (just an inch or so) in it while it dries. I use a long cardboard tube from some wrapping paper to do this and I've found it really helps stop the paper going wavy.
I've also been known to leave A4 prints on top of the vents of my monitor to speed up the drying process...
Oh, and check you have the correct paper type selected since this problem can come from putting too much ink on the page.
Here is a link to some directions for hot dry mounting: http://www.itg.uiuc.edu/help/drymounting/#Materials. These can be used for some ink jet prints. I have some prints made from an Epson 1270 a few years ago that look fine. You may have to play with this a bit though and some say you shouldn't use it for ink jet prints (Like I said though, I have used it and been happy). The equipment is expensive if you only are mounting a few prints. Some places such as frame and matting stores will do this for you or allow you to use theirs.
You can also get paper for a cold press. It is basicallly like double sided sticky paper.
If you are interested in how archival this will be try Wilhelm Research (Their site is temporarily down, but they are the experts in this).
I wonder if this is a climate thing. Out here in 14% relative humidity, any of the Epson premium super B paper comes through my printer without any waves or curl.
Which paper are you using? If it's a lightweight photo paper (the kind I use for proofing only) you might try the heavier resin coated papers like Premium Glossy or Premium Semigloss. If you have the matte black cartridge, try Enhanced Heavyweight Matte (AKA Archival Matte). The lightweight stuff like Epson Photo Quality Inkjet Paper and Glossy Photo Paper are not acid-free and are a poor choice if you want the archival prints the 2200 offers.
I do have to battle to get the curl out of roll paper. The best method I've found is to back-roll the prints around a cardboard tube and keep it in place using a few rubber bands. Let the paper form to a new shape overnight and most of the curl will be gone. I use two pieces of thick foamcore board to sandwich prints. Use spring clamps to hold it all together and give the prints a few days to relax. I recommend you try roll paper if you haven't. The cutter with the 2200 and roll paper makes for a very versatile paper output solution.
Actually, the State of Washington is more like 95% humidity.
Of course, it rained today. I have only bought the paper which goes with the 2200; Archival Matte, Luster, and Semi-gloss. Those are in 8-1/2 x 11. The one I used for the 13x19 prints was their Watercolor Matte.
I have tried putting the print between two sheets of cardboard (the kind that comes in the printing paper package). I have tried drying on the t.v. and also putting in between two newspapers.
There are some other ideas here I may try. I was thinking back on my B&W developing days (25-30 years ago) and how we used a blotter roll. If I could find a big enough one....
Thanks for all the help.
"Today is the tomorrow that yesterday you spent money like there was no."
Yep, it sounds like humidity. My prints on Radiant White Watercolor came out perfectly flat. Dry time is negligible here. Any chance you could store your paper and prints in a room with refrigerator AC or a dehumidifier?
For blotter paper ask a college art department printmaking shop. That's a staple supply and they are sure to have a source they could recommend.