System Center Forum has posted a PowerShell script that will allow you to submit a wildcard filter based on device IP address to update the proxy agent for all SNMP-enabled devices matching the filter. This will allow any SNMP-enabled devices to be monitored from any management server or agent-managed computer.
You can access the script at:
http://www.systemcenterforum.org/news/powershell-updating-proxy-agent-for-multiple-snmp-enabled-devices-part-1/
Marco Shaw published a Part 2 follow-up to this post with improvements to the original script.
You can find it here:
http://www.systemcenterforum.org/news/powershell-updating-proxy-agent-for-multiple-snmp-enabled-devices-part-2/