I tried using the boot strut from my old BWM. It put too much pressure on and lifted the boot on that side.
I did find a solution for the springs tho. Take a piece of wood/plastic/metal about 5cm x 2cm x 2cm high (you may need to play with height, depending on the amount of slack you have)
Cut a small notch the width of the spring bar across the top:
---u--- Side view
## Top view
Sort of like that if you can imagine it.
Make one for each side. Now comes the dangerous bit. There is a real chance of taking off the end of your finger if you are not careful.
Use something to lever against the bit of spring that is sticking out at the back (I used the handle of a large wrench), and lift up the front bit of the spring. Slip the block under the bar where it sits on top of the hinge. Carefully lower the spring back onto the block. Repeat other side.
This puts a little more pressure on the spring bar, and will hold the boot open. It may not last for ever, but has done me well for a few months now.
I will try and get some pics of it in action.