Balance 20x on 4g only integration with 2HA configured Balance210's

Hi

How do I integrate a 4g link (A) ( want this to be separate) sitting on a balance 20x , with a stack of (B) Balance210’s Speedfusioned into core 1350s ).
What I want to achieve is basically use the 4g connection (A)( different vpn tunnel ) to access the LAN side of (B). THey are all on the same subnet