Did a bit of this back in the day - you know, somewhere around Photoshop 3...
Used to call it 'cross-processing' 'cos you're using E6 film processed in C41 chemistry, and vise versa. Results were a bit hit & miss if I remember - lots of experimentation required - but gave interesting results when it worked. Seem to remember it tends to over-process a bit, so best to under-expose initially.Never processed my own C41 so can't advise there I'm afraid. Might be worth finding a decent lab (if they still exist of course) and asking if they'll cross-process?? Try Googling 'cross processing' as well of course - I'm sure you'll find plenty of info.
HTH, Pete.
