Great idea, I think I am going the same route with a longer pin passing through a hole in a hockey puck.This is what I ended up with. I got a Golf/Passat/Vento A3/A4/A6 jack and then welded a pin to it that fits the C5. It is rated for 970Kg (~2117 pounds).
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yes it works great.
This was discussed recently..
You could look for a small aluminum(!) jack from a Mercedes or an Audi.
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I think Frank on here bought two recently and had an extra!
I carry this jack,a plug kit and small compressor in my C5.
Graham