Is it possible to extend indexers in PowerShell?

Question

PowerShell's type extension facility is neat, but I haven't yet figured out the way -- if one exists -- to extend an indexer. I've tried to add a ScriptProperty for the indexer property (Chars in the case of System.String) and a ScriptMethod for the getter (get_Chars), but neither approach seems fruitful. Is it at all possible, or am I wasting my time? :)

[Edit] Apparently the proper member type is ParameterizedProperty, but when I try that, I get:

Add-Member : Cannot add a member with type "ParameterizedProperty". Specify a different 
type for the MemberTypes parameter.

At line:1 char:11
+ Add-Member <<<<  -MemberType ParameterizedProperty -Name Item -InputObject $string { "x" }
+ CategoryInfo          : InvalidOperation: (:) [Add-Member], InvalidOperationException
+ FullyQualifiedErrorId : CannotAddMemberType,Microsoft.PowerShell.Commands.AddMemberCommand

Answer 1

I'm going to conclude that the error message I'm getting is the final word on the matter. Also, on further reflection it has become obvious that the sort of extending I was hoping for is not supported by this mechanism anyway. :-)