Your question isn't clear - what is the 'config file' that you want to put this in?
You have two types of maps in IOS that you might be confusing:
e164 maps: allow mapping multiple destination-patterns to each dial peer
server groups: allow mapping multiple session-targets to a dial peer
It may be the server groups feature you are looking for (http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/dialpeer/configuration/xe-3s/vd-xe-3s-book/multiple-server-groups.html)
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