How to configure fixed nexthop destination for smtp in master.cf

[Michael Storz]

I am trying to configure a fixed destination for a smtp transport in 
master.cf instead of confguring the destination in a transport_map. 
Since smtp has no special command-line option for this I suppose I have 
to specify a generic Postfix daemon option via -o. However, since all 
relevant commands in main.cf like default_transport include a transport 
field, but transport has already been choosen when the email arrives at 
my smtp transport, I have no idea how to configure this in the correct 
way.

Michael