Let's say you have a time series in a column (maybe output from 3dmaskave). You could use 3dcalc to put the 1D time series file back to fill up the grid of a 3D time series dataset like this:
3dcalc -a epi_r1+orig -b col1.1D -expr 'b' -prefix ts3dcol
3dUndump can be used to fill in particular xyz/ijk locations with specified values or fill in all voxels with a default value.