Android usb sharing/tethering support routing mode

Dear all gurus

I would like to make sure one thing,

Does the android usb sharing / or tethering support routing mode?
I need a private fix ip for enterprise users , and routing mode , NOT NAT mode.

This is a quite common user case , "3G/4G backup the adsl line"
For enterprise users ,
there is a network device (network gateway) attached a usb android data card,
the gateway also has an adsl fix line connected , when the fix line down ,
the usb data card will automatically dial-up to the 3G/4G network
However we need the usb interface is Routing Mode , NOT the "NAT mode" ,
'cause when the backup dialed into is a private VPN environment.

We feel the data card firms seems NOT willing / able to do this modification ??!!
There is also a key issue , when the data card dialed up ,
the mobile operator has to assign a fix private ip for that gateway device (RADIUS Op).

ps: the 4G environment is quite VERY differ than 3G , whenever the usb interface is "POWER provided"
the 4G network also is CONNECTed !

Any answers will be appreciate.

thanks !