Question re: sewing stretchy (t-shirt) material

[great-stoneface.livejournal.com]

Sorry if this has been addressed before, I didn't see it in the memories.

I'm planning on making a t-shirt pillow (from the instructions here), but I have one problem. My mom's my sewing teacher, and neither of us have any idea how to sew t-shirt material/other stretchy fabric. Any tips? I'll be sure to post pics of this project when I get it finished, as well as my twelve billion other WIPs.

Thanks!