Can I run Export-SPWeb from another machine using PS Remoting?

I'm trying to run SharePoint Export/Import from a remote machine. I can get it to work if I remote on to the individual box, but want to run it from another machine. I’ve enabled PSRemoting on each box, but I’m getting command not recognised errors. So, when I run:

Invoke-Command –ScriptBlock {Export-SPWeb –Identity $SourceIdentity –Path $Path –ItemURL $ItemUrl} –ComputerName $SourceComputer

I get:

The term Export-SPWeb is not recognised as the name of a cmdlet, function, script file or operable program. ......

I’ve tried running:

Invoke-Command –ScriptBlock {Add-PSSnapin Microsoft.SharePoint.PowerShell} –ComputerName $SourceComputer

Beforehand but it makes no difference. Is what I’m doing possible, and if so, what am I not doing?

Thanks