(2) ISPs, (2) DHCP servers, (1) LAN?

[GMGQ]

So here's what I have:
(2) ISPs, so (2) modems
- ISP#1 hooked up to a DI-624 Router
- ISP#2 is also connected to the same LAN via a switch, but only (1) computer on the LAN needs access to it (that computer is too far away from where this modem is plugged in, so connected this 2nd modem to the LAN is the only way)

ISP #1:
- All but one of the clients have been assigned a STATIC IP
- The one exception is a VOIP box, because it's just plug and play. Meaning there's no way for me to 'get in' to the box to configure it with a Static IP. It will only accept a DHCP IP. Therefore I must turn on DHCP on my router. The best I can do is make (1) IP available, and configure the router to always assign that IP to the VOIP box (via it's unique MAC address).

ISP #2:
- Only one computer is connected to this ISP
- the MAC address of this one computer has been added to this ISP's account (it's ADSL)
- That one computer has (2) NICs in it: (1) for connecting to ISP#2, (1) for connecting to the LAN
- ISP#2 gives me a Dynamic IP, so NIC#1 on this computer must be configured for DHCP
- NIC#2 configured with a STATIC IP to communicate with the LAN

So my problem is that both the VOIP box and the computer on ISP#2 are configured for DHCP. Therefore whenever I reboot that computer, when it comes back on, it immediately searches for an IP from the ROUTER. But the router is configured to only assign a certain IP to the VOIP box's MAC address. So it keeps denying the other computer.

I have to log into the router, DISABLE DHCP for a few seconds, then the other computer will successfully grab an IP from ISP#2. Once that has happened, I can re-enable DHCP on the router, and the VOIP box will get it's IP from the router.

So what I'm wondering is if there is any way to get the computer on ISP#2 to ONLY look for ISP#2 for a DHCP IP? Is there any way to stop it from going to the router first? I've tried going into that NIC#1's properties and setting the Default Gateway to that of ISP#2, and I've tried setting the DNS to that of ISP#2, but that doesnt work. Suggestions??? Thanks in advance.