Are you bringing them to use on the plane or in the hotel? On the plane, I'd suggest investing about $10 in one of those u-shaped neck pillows (I got mine at Walgreens) and 'wearing' it onto the plane - I don't think they count it as anything that way.
If you're bringing your pillows to use in your hotel room, get one or two of those space-bag things; put the pillows in them and squeeze/vacuum out all the air, then pack them in your suitcase.