Hi Juergenrieger 
This is not possible, you just need to configure the Remote PIX with the address
of the Central PIX, but on the Central PIX you would need to set the ISAKMP peer
with 0.0.0.0 netmask 0.0.0.0. 
isakmp key  address 0.0.0.0 netmask 0.0.0.0 (Central site)
isakmp key  address  netmask 255.255.255.255
The remote PIX must initiate the connection as this knows about the PEER where the
Central site does not, this has been configured to dynamically accept connections from anywhere knowing the wild-card pre-shared key.
Regards MJ