Hi Daniel,
Thanks for your response. Unless I don't quite understand how to set things up, I don't think the -mask SELF option would work because that would simply take the entire functional image and mask itself but it wouldn't let me focus on the ROIs. Here's how I originally tried setting it up (res_COPY_${subj[$n]}T1.2.zp.nii has the hand drawn ROI, the ROI has a value of 1, and r${subj[$n]}${scans[$scan]}_0000_GrandAvgwo156LPI.nii is the functional image):
3dmaskave -mask res_COPY_${subj[$n]}T1.2.zp.nii -mrange 1 1 -dump \
r${subj[$n]}${scans[$scan]}_0000_GrandAvgwo156LPI.nii