You can't specify the channel file in this way. You pass a data file, and the batching system will fetch the associated channel file automatically.
Do not try to edit the contents of the sFiles structure. In most case, only the .FileName field will be read by the target process. To avoid any confusion, I'd recommend you only use sFiles as a cell array of input files ("data" files only for process_headmodel), as in the scrits generated automatically by the Pipeline Editor.
If not, probably I would do as you suggested that I will quickly import some dummy EEG recordings just for running the head computation because the EEG hasn't been cleaned yet.
This is the only way to go.