I have modified 3dttest to have an option to generate a second dataset, which will contain the approximate DOF computed at each voxel. You can use this 1-brick dataset to adjust the t-statistic (2nd sub-brick of the "standard" output) in some way. The command lines you would use would be something like

3dttest -unpooled -prefix tt -dof_prefix tt_dof -set1 ..... -set2 .....
3dcalc -a 'tt+orig[1]' -b 'tt_dof[0]' -datum float -prefix tt_zz -expr 'fitt_t2z(a,b)'
3drefit -substatpar 0 fizt tt_zz+orig

The first line shows the new -dof_prefix option, which when -unpooled is active, says to save the DOF into dataset with prefix tt_dof.
The second line is a 3dcalc command to convert the t-statistic and the DOF parameter into a z score. The third line labels the output as a z score.

The source code for this is available now. Binaries are being compiled and will be on the Web site sometime this p.m.

bob cox