Your chandler can supply a fitting that is bolted and clipped up the mast at the height you require and the wire stay is swagged to this fitting. The bottom end has an adjustable pelican hook (or similer) and this is attached to the stem fitting or an eyebolt through the deck (suitable strengthened, if possible onto a bulkhead) via a wire pendant made up to the appropiate length and tightened. When not in use the pelican hook is attached to an eye on the mast or a shackle on a shroud chainplate etc. where it is out of the way. Keep the wire pendant in the bag with your (hanked) storm jib.
I have used this system for the last 8 years and it is very easy to use and stow. As I am away from my boat I cannot give you the manufactures name but I am sure that all sparmakers produce them
I'd suggest having the fitting on the mast relatively close to the masthead (how far down depends on the strength of the mast) so as to avoid tangling with the furler whilst allowing you to sail without running backstays. The eye on deck should be situated at a bulkead so that a chainplate can be fastened to it. The best system for the bottom of the stay is with a Norseman/StaLok fitting to a rigging screw connected to a "sliphook" (Gibb used to have them; don't know about the present situation in the UK in that respect, but you could get it from "www,westdiep.com"). With a bit of luck, you might end up as I did: the inner forestay minus sliphook and rigging screw arrives one inch above the deck just forward of the lower foreshroud, so I make it fast it there with a bit of line.