Inner Forestay or not

Would love to go to the Southampton boat show but unfortunately its a bit far for me from New Zealand.

Below is a post regarding an inner forestay set up with running backstays on a 470. I think your method is fine too however it would be nice to have the runners in a big blow for the extra mast support.

I've pinched a photo from the forestay removal topic which isn't straightforward shot of where it leaves the mast but I'm sure you'll soon understand.

The Spinnaker pole uphaul, I think they call it, I've used the pulley (same type as the halyards for the main, jib and spare that I fly both code 0 and gennaker).  I've run Dyneema  down to the deck and through a pulley then back up to a mount secured to the mast just below the pulley.  So out of the mast down to the deck and back up to the mast, (which I move out of the way and clip at the base of the mast when using the self-tacker).

The J3 isn't hanked on the pulley's fitting is passed through the clew and the whole thing is hoisted and pulled tight, sheets lead to the jib car tracks left and right. If as you say mast pumping starts, like a resonating halyard that's too tight, I can ease it allowing the pulley to roll slightly to act as the shock absorber.

I can't draw on this as its within the forum system already, but you can see the Dyneema coming down from the mast to the pulley attached to the deck (standing rigging for now), round the pulley and heads back up to the bracket fixed to the mast (2:1). 

I fed a length of Dyneema from the blocks in the cockpit through the deck tidy and up the mast to the pulley, down and back up again. Same as all other halyards.