When I need to execute a query with parameters I just create a PowerShell script for that specific purpose and load LibrarySmo at the beginning of the script. Here's a simple example.
$scriptRoot = Split-Path (Resolve-Path $myInvocation.MyCommand.Path)
$srcServer = 'Z002\SqlExpress'
$qry = @"
SELECT * FROM dbo.authors
WHERE au_lname = '$au_lname'
Get-SqlData $srcServer 'pubs' $qry
To execute save the code as a ps1 file (here I'm using getAuthor.ps1). You'll also need to change the $srcServer variable or add it as a parameter to script and pass the server name.
Also when I need to load the contents of a file such as a .sql file, I'll use the .NET ReadAllText method:
$qry = [System.IO.File]::ReadAllText("c:\users\u00\scripts\pubqry.sql")
As far Get-Help, eventually I plan on creating a proper snapin with Get-Help functionality in a future release.