OpenVPN, resolvconf, and DNS domain resolution

While at site1, I need to connect to site2 via OpenVPN. Once connected, the OpenVPN site2 pushes a DNS nameserver and domain search options. This causes all name resolutions for site1 to fail.

Example:

1. Physically connected at site1, DHCP pushes DNS options and resolvconf manages them.
   /etc/resolv.conf

   # Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
   #     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
   nameserver 172.16.1.101
   nameserver 172.16.1.102
   search site1.internal.domain
   

2. Open OpenVPN tunnel to site2, OpenVPN pushes dhcp-option DNS and DOMAIN for site2 and /etc/openvpn/update-resolv-conf pushes them to resolvconf.
   /etc/resolv.conf

   # Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
   #     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
   nameserver 192.168.1.5
   nameserver 172.16.1.101
   nameserver 172.16.1.102
   search site2.internal.domain site1.internal.domain
   

3. DNS resolution works for server.site2.internal.domain but fails for server.site1.internal.domain

Is there a way that any failed DNS request to site21 should fall-through to the site1 DNS servers? Or configure resolvconf that only queries for site2.internal.domain should be passed to the site2 nameserver?

I use an Ubuntu 14.04 machine at site1, and the OpenVPN server at site2 is a pfSense 2.2 box. I manage both sites so making changes to either side isn't a problem. Both domains are non-public and internal use only.