I use the mechanical lift on my 2305 also. Note also than when doing this you still CAN use the 3pt hitch for some implements even when you are running the deck. The key is that you adjust the deck and lower it to the stops. You'll have the range from all the way down to when the deck starts to lift (Doesn't start to lift until the top of the 3pt hitch range) to use the 3pt hitch. Takes a little getting used to but you can do it even while using the deck. I mount my Cyclone rake on the 3pt hitch while I have the mower on and this works fine since I keep it in the middle of the 3pt range (Before it starts lifting the deck).
If you aren't running the deck you can use the 3pt hitch for anything you want. Just keep the left/right adjusters set so the lift lever for the deck doesn't 'fall' off the lift arm. (You don't need the spacer rod if you use an implement). It's also better to lock the deck in the up position when doing this.
But JD now is offering (in their printed catalog) a 3rd SCV for the 2320 and 2520, could a 3rd SCV for the 2305 be far behind?
Someone on this site did post a product (can't remember the company) that basically was electric diverter valves and gave you I think 2 additional SCV's. It had a Video Game like handle with buttons that replaced the knob on the Dual SCV control lever.