This has been discussed quite a bit. You might start with: innerstay
But to summarize the option you suggest is the easiest/cheapest but probably the least effective of the possibilities.
The problems with it are #1 not enough stay tension to get a straight luff and be able to sail to windward. You can improve this by making the halyard a 2:1. #2 Its a bit clumsy and a bit unsafe because when you are hanking on and hosting (and dropping) the stay is not tensioned and flopping around on the foredeck. #3 The halyard sheave, clutch
are probably not sized to hand the shock load involved when the mast
whips (When you are pulling to windward into waves), #4 you need to modify your stay sail to make it work, adding a high modulus rope
in the luff.
One better options is to put a strong tackle at the bottom of the dyneema
stay. Colligo marine
has some hardware
specifically for doing this.
Another solution (I think developed by Rod Stevens and used on many swans) is to have a curved fitting on the side of the mast
(or on the stay), where you hook the stay and then the lever (or turnbuckle) forward to latch onto a deck fitting. This keeps everything tight and neat when the stay is stowed.
Another solution is a 2:1 halyard with a staysail on a 'code zero' continuous line furler
. This is very neat but the most expensive of the options.