No. It is not possible to directly call a sequence for any of the substeps (Edit, Pre or Post). The sequence adapter is not available for calling substeps, and there is not current plans to add this ability.
You could call code (VI, DLL, ActiveX server) using one of the adapters available for the substeps, and then within that code you could call a sequence using the NewExecution method. I would only do this if it was really necessary.