I was hoping Teodora's answer would work...I get a headache thinking
about this.

Okay, lessee what I can come up with...

to3d the data into the afni world in a rotated but correct size
coordinate frame. That is, a frame that's the same size as
your stack of slices, but rotated 11 degrees.

3drotate the BRIK 11 degrees.

3drefit the HEAD to contain the proper dimensions for the new BRIK,
based on the location and orientation of the original data and the
rotation in the previous step.

I think those steps will be enough. And I think that may be the
easiest way to do it. Now you just need the proper numbers
for each step. And you may want to wait for some person
who knows something about this to correct any errors I've made.