I don't have a Wemo and don't know much about it, but I assume each one has its own IP address? You will need to know which device has which IP address.
You could then create a payload xml file in which each Wemo's IP address is associated with a friendly name, like "corner light", "kitchen light" etc. (example file is attached)
Rather than just saying "Turn wemo on" or "off". You then specify which one when issuing your command. Within the command, VC will refer to your payload XML file to find the correct IP address for that friendly name.
<?xml version="1.0" encoding="utf-16"?>
<!--VoxCommando 2.0.0.0-->
<commandGroup open="True" name="wemo" enabled="True" prefix="" priority="0" requiredProcess="" description="">
<command id="758" name="Turn wemo on" enabled="true" alwaysOn="False" confirm="False" requiredConfidence="0" loop="False" loopDelay="0" loopMax="0" description="">
<action>
<cmdType>Scrape.Post</cmdType>
<params>
<param>http://{1}:49153/upnp/control/basicevent1</param>
<param><s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/" s:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"><s:Body><u:SetBinaryState xmlns:u="urn:Belkin:service:basicevent:1"><BinaryState>1</BinaryState></u:SetBinaryState></s:Body></s:Envelope></param>
<param />
<param />
<param>text/xml; charset="utf-8"</param>
<param>SOAPAction: "urn:Belkin:service:basicevent:1#SetBinaryState"</param>
</params>
<cmdRepeat>1</cmdRepeat>
</action>
<action>
<cmdType>OSD.ShowText</cmdType>
<params>
<param>{LastResult}</param>
</params>
<cmdRepeat>0</cmdRepeat>
</action>
<phrase>Turn</phrase>
<payloadFromXML phraseOnly="False" use2partPhrase="False" phraseConnector="by" Phrase2wildcard="anyone" optional="False">wemoDevices.xml</payloadFromXML>
<phrase>on</phrase>
</command>
<command id="766" name="Turn wemo off" enabled="true" alwaysOn="False" confirm="False" requiredConfidence="0" loop="False" loopDelay="0" loopMax="0" description="">
<action>
<cmdType>Scrape.Post</cmdType>
<params>
<param>http://{1}:49153/upnp/control/basicevent1</param>
<param><s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/" s:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"><s:Body><u:SetBinaryState xmlns:u="urn:Belkin:service:basicevent:1"><BinaryState>0</BinaryState></u:SetBinaryState></s:Body></s:Envelope></param>
<param />
<param />
<param>text/xml; charset="utf-8"</param>
<param>SOAPAction: "urn:Belkin:service:basicevent:1#SetBinaryState"</param>
</params>
<cmdRepeat>1</cmdRepeat>
</action>
<action>
<cmdType>OSD.ShowText</cmdType>
<params>
<param>{LastResult}</param>
</params>
<cmdRepeat>0</cmdRepeat>
</action>
<phrase>Turn</phrase>
<payloadFromXML phraseOnly="False" use2partPhrase="False" phraseConnector="by" Phrase2wildcard="anyone" optional="False">wemoDevices.xml</payloadFromXML>
<phrase>off</phrase>
</command>
</commandGroup>
If you're not yet familiar with payload xml and how that works, you might want to watch the Vera \Home Automation tutorial video. A lot of the explanations apply generally in VC, whether or not you're using the Vera plugin.
Here is a master list of available video tutorials:
http://voxcommando.com/mediawiki/index.php?title=Video_Tutorials. You should also watch the Fundamentals videos on editing commands.