combining data collections to enter into the System Identification Toolbox

Hi

I have a number of data collects. The fist column of the matrices are the number of seconds (one second sample rate) and the remaining columns are temps from different thermo-couples. Each matrix has a different number of rows (they were run for different time periods), but the same number of columns (the number of thermo-couples never changed). They each represent the same system, each one under different starting conditions. I'd like to enter these matrices into the System Identification Toolbox. I haven't been able to figure out the merge routine yet, but it looks like it might be the way to go once if I could get it figured out. Any suggestions? Thanks...