Apparently you have been able to do this since December 22nd 2008. Christian Glessner wrote a WCF Proxy generator.
The original blog post in which he described it is here. He also posted the script in this PoshCode.org post.
I updated the code to Powershell v2. I'd suggest using that version. I talk about my version on this blog post.
If you use that code, dotsource it from another script, don't include it inline. Here is an example using my version of the code:
# My example WCF service:
# https://github.com/justaprogrammer/EchoService
. .\wcf.ps1
$wsdlImporter = Get-WsdlImporter 'http://localhost.fiddler:14232/EchoService.svc/mex'
Get-WsdlImporter 'http://localhost.fiddler:14232/EchoService.svc' -HttpGet
Get-WsdlImporter 'http://localhost.fiddler:14232/EchoService.svc?wsdl' -HttpGet
$proxyType = Get-WcfProxyType $wsdlImporter
$endpoints = $wsdlImporter.ImportAllEndpoints();
$proxy = New-Object $proxyType($endpoints[0].Binding, $endpoints[0].Address);
$proxy = Get-WcfProxy 'http://localhost.fiddler:14232/EchoService.svc/mex'
$proxy.Echo("Justin Dearing");
Get-Help Get-WsdlImporter
Get-Help Get-WcfProxyType
Get-Help Get-WcfProxy