Multiple Showerheads..... Is there any problem with this plan? New Shower enclosure (no tub). I want two shower heads. They will NOT be both used at the same time, just one or the other. Can I install one mixer valve, then Split the outlet line to the two shower heads with a simple shutoff valve at each shower head?. Seems simple enough. Just looking to have the option of either shower head, without getting complicated and keeping the cost down. Any reason this would not work? Thanks for your help.