So I'm finally getting back around to this and I'm having issues with it. I'm trying to invoke this method from Powershell and it's partially working, it's setting the package to All Package Servers rather than the individual servers specified. Also invoking the method from the asmx page gives me more errors.
$ns = new-object -comObject "Altiris.ASDK.NS.SoftwareDelivery.SWDSolnPackageManagement"
$ns.TargetServer = $server
$ns.authenticate()
$pc = $ns.GetPackageExByGuid('7c19b03a-e172-4cec-a906-ad7b648a2f7f')
$list = $pc.selectedpackageservers, "3B72E021-74AA-4B19-9C79-023E8F9AC392"
$ns.SetPackageExPackageServerOptions("7c19b03a-e172-4cec-a906-ad7b648a2f7f",$false,$list,"c:\test")