Bypassing the captive portal for devices that need to?

Hello all, 

First I will give you my set up:

From the internet connection I have a TP-Link dual WAN router that feeds into a SG105 on eth1. From the SG105 the eth0 and eth2 interface connect to a switch (There is a reason for this). The switch then feeds the AP's (EnGenius  ENH710ext's if it makes a difference). 

The reason for having two connections from the sg105 to the switch is I have set up a primary gateway with a captive portal for normal traffic from PC's and android/iOS devices. The second connection is the reason for this posting, I would like to have a second gateway address for devices like Roku and XBox to allow them out to the firewall without using the captive portal. This would of course be filtered by MAC address and the device would have a static IP assigned to it. I currently am using two DHCP servers on the SG to accomplish this. One with the normal scope and gateway, the other having static reservations for the devices using MAC with a different gateway address. 

My question is am I approaching this properly? Will this work? 

I currently have been able to get the appropriate IP address on a device but it still goes to the captive portal. I might be missing something in the config. (static route perhaps?)

Any questions comments are welcome, but please don't troll. 

Thanks for any help supplied.