routing based on switch port - is that possible?

Hi all,

I run an EdgeRouter X  with a pretty simple configuration:

WAN side:

eth0 - ISP1

eth4 - ISP2

LAN side:

switch0 (eth1,eth2,eth3), 192.168.1.0/24, dhcp on switch0

I need to create a routing policy based on source swith0 port - i.e. , clients connected to ethernet ports eth1 and eth2 should go to the internet via ISP1, and  clients connected to eth3 should go via ISP2.

What I mean is something similar to EdgeMAX - Policy-based routing (source address based)    - just  not "source address based", but "source ethernet port based".    At the same time I prefer to keep existing LAN as simple as it is configured now. 

Is that possible?  

Appreciate your help,

Michael.