Is it possible to make such a connection to ddwrt?

Question

Network administration

Hello colleagues!
One organization has a DIR-300 on which Internet authorization takes place. the organization has its own Internet 100 meters away and there is asus rt-16 with dd-wrt. These organizations are united, and the Internet needs a common one (where dir-300 is), but they should not see each other's computers.
There is an idea to do it this way:
from the DIR-300, throw a wire and connect it to WAN on ASUSe, and then select a DHCP connection instead of PPPOE. But not sure if this will work?
Or maybe do something differently?
I would be grateful for any advice!