I would not do that. I think you might get some staining problems from the fixer but I'm not sure. Permawash is relatively cheap so use separate baths. If you have space issues, consider single tray development. That is what I do.
I think it is cheaper up front to use plain selenium toner without PermaWash but you will spend alot of time dealing with filtering the solution, cleaning up stains, etc. Time is money and I prefer using one shot selenium toner and toning in batches.