I have this exact combo on my plane (VP-X and S2000 starter switch) and it works well.
I ended up using a secondary 12V relay from the autoparts store.
One thing to be careful with, is that it matters which side of the s2000 switch you send power to. I had to have have an electrical engineer buddy with an ocilliscope come and help me troubleshoot some weird starter issues I was having.
When we switched around the leads on the s2000 switch, everything worked fine. Below is a sketch of the wiring diagram I used. Take a look at some of the s2000 intallation DIY guides to determine the direction to send power through the switch and you should be fine.
Hope this helps,
Jason
