I started mucking around with PS and the BESUserAdminClient, but have had problems getting the tool to exit properly from PS (it just stays open):
$psi = new-object System.Diagnostics.ProcessStartInfo("C:\Program Files\Research In Motion\BlackBerry Enterprise Server Resource Kit\BlackBerry Enterprise Server User Administration Tool Client\BESUSerAdminClient.exe");
$psi.UseShellExecute = $false;
$psi.Arguments = "-add -u or whatever arguments you want to add";
$psi.Domain = "AD Domain";
[System.Diagnostics.Process]::Start($psi)
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