Raising an old thread but did you ever get an answer to this ?
I too have a DS410 and this question has just popped in to my head but for a slightly different reason.
With the release of DSM 4.2 i switched my dhcp server role to the DS to make use of the PXE server which works but obviously i need to use an Ethernet connection to boot to it, however i dont always have the DS on and have been caught out a couple of times with no DHCP - I know i could use static IPs but i would rather have things automated for any new / temp clients.
I wanted to retain the ability to use my PXE server but use my always on routers DHCP server - going through available options i can see that the PXE/DHCP server config on the DS offers an interface selection - if i could have a second NIC and selected this as the PXE enabled DHCP interface i could still run my routers DHCP and have a dedicated link for performing PXE boots.
So did you find anything ? If not i will have to try one when im back at home, i have a usb NIC kicking around somewhere , just didnt want to waste my time if someone already has the answer and it very well could be you !