Dear Alfonso,
Thank you for your answer, that's exactly what I'd like to do.
The first proposition is not really a option because the onsets of each condition differ across sessions and subjects (that's why I need to import the SPM.mat).
The "conn_importspm(..)" command might be what I need but I didn't really understood how can I implemented it in my batch (attached) (i.e., right after Batch.Setup.spmfiles? Instead of Batch.Setup.done?).
Or maybe another alternative could be to specify a name for the spmfile of each session? (something like "Batch.Setup.spmfiles.names"??).

Thanks you very much for your consideration,
Pauline