3g dongle directly to LAN

I have mobile internet with possibility to have dynamic public ip address.
I want to turn off dhcp and to have this public address provided to computer connected with lan to openwrt router with 3g dongle.

I have already bridged wifi master and eth0. But i feel i can not bridge with them also 3g interface?
Lan has static address 192...., public address on 3g is 78.......

How to forward this address 78...... so connected pc will have also this adddress?

May be you should consider port forwarding?

do you mean I make port forward rules like:

(the eth0/wifi has address 192.168.1.1 - so I can SSH it, DHCP enabled, eth0 is bridged with wifi master AP)

"port forward 443 from wan (78.x.x.x) to lan IP 192.168.1.100 port 443" ?

I set up DHCP only for 1 client so I know the address of this connected PC will be 192.168.1.100?

Yep, like that.

LuCI > Network > DHCP and DNS > Static Leases

I tried it and finally it works! I use it for SoftEther project.

if I can one more question: I feared to do some stupid setting and then to loose access to router so I decided this safe way with DHCP...

if I turn off DHCP then PC computer must have static address? So my router eth0 is 192.168.1.1 and PC will have 192.168.1.100 static address? this will work? I never set up static leases yet I must study it first, what is it?

Yes.

DHCP-server provides IP-address based on client MAC-address.