To set proxy addresses in Live@edu, I had to change this:

PCommand.AddCommand("Set-Mailbox");
PCommand.AddParameter("Identity", emailName);
PCommand.AddParameter("MailboxPlan", "GalDisabledMailboxPlan");
PCommand.AddParameter("EmailAddresses", sProxyAddresses);

To this:

Dim addresses As New ArrayList
addresses.Add("SMTP:" & emailName)
addresses.Add("smtp:" & sProxyAddresses)

PCommand.AddCommand("Set-Mailbox")
PCommand.AddParameter("Identity", emailName)
PCommand.AddParameter("MailboxPlan", "GalDisabledMailboxPlan")
PCommand.AddParameter("EmailAddresses", addresses)

Thanks to: http://powershellcommunity.org/Forums/tabid/54/aff/3/aft/195/afv/topic/D...