An update cause I finally found time to change the plate.
I tried this solution
![](http://images6.thomann.de/pics/prod/178843.jpg)
(2euros from a German on-line shop).
The plate fits great and the extra part with the sharp edges stabilizes to the wood and the jack i solid!
Here's a pic:
![](http://lh3.ggpht.com/_eV5RciErQzw/TTvyQ8LQw5I/AAAAAAAABaE/XtbPo4ULkv4/100MEDIA_IMAG0249.jpg)
thanks again all for your help - suggestions!