Add IIS 8.5 Custom Logging Fields with Powershell - iis

Question

Windows Server 2012 R2 with IIS 8.5 allows for custom log fields with Enhanced Logging
http://www.iis.net/learn/get-started/whats-new-in-iis-85/enhanced-logging-for-iis85
I want to add the fields with Powershell
The following works:
Set-ItemProperty IIS:\Sites\siteName -name logfile.customFields.collection -value
#{logFieldName='foo';sourceType='RequestHeader';sourceName='c-ip'}
But I cannot add a second entry to logfile.customFields.collection It requests -Force and overwrites the existing entry
I added 2 via the GUI to illustrate the issue
Get-ItemProperty IIS:\Sites\siteName -name logfile.customFields.collection
logFieldName : foo
sourceName : c-ip
sourceType : RequestHeader
Attributes : {logFieldName, sourceName, sourceType}
ChildElements : {}
ElementTagName : add
Methods :
Schema : Microsoft.IIs.PowerShell.Framework.ConfigurationElementSchema
logFieldName : foo2
sourceName : c-servername
sourceType : RequestHeader
Attributes : {logFieldName, sourceName, sourceType}
ChildElements : {}
ElementTagName : add
Methods :
Schema : Microsoft.IIs.PowerShell.Framework.ConfigurationElementSchema
logFieldName, sourceName, and sourceType are NoteProperty Members with the same name
How do I do this in Powershell?

Answer 1

A user on the IIS Forums answered
New-ItemProperty IIS:\Sites\siteName -name logfile.customFields.collection -value
#{logFieldName='foo';sourceType='RequestHeader';sourceName='c-ip'}
New-ItemProperty IIS:\Sites\siteName -name logfile.customFields.collection -value
#{logFieldName='foo2';sourceType='RequestHeader';sourceName='c-ip'}
I confirmed this does work