Adding a second Network Adapter to the Virtual Machine is the easy part as that can be done thought the UI under the Setting for the target Virtual Machine however the second part cannot be done through Fusion by itself and requires modifying the boot.sh file and the target Virtual Machine's .vmx configuration file. This can be done totally manually or through the use of Advanced Networking Configuration - Tokamak Networking Scripts for VMware Fusion and manually editing just the target Virtual Machine's .vmx configuration file.

You can also look at the following as a reference as well: How to tell Fusion which Host Network Adapter to use.pdf

So are you saying you have read and followed the directions at ...

VMware Fusion (menu bar) > Help > VMware Fusion Help > Managing Virtual Machines > Configuring the Network Connection > Adding a Network Adapter

... and it doesn't work?