Sure, how about sending them a text message containing a hyperlink that allows them to download the task in a manner that can be imported into their local schedule?
O.K., let's go over this from the top. What mechanism have you been using (before your Android/iPhone migration) to publish tasks out to your employees?
Before you migrated to smartphones, what mechanisms were you relying on to publish tasks? I'm implicitly assuming that Office didn't implement a "calendar groupware listener," in the spirit of, say, an ORACLE listener. Can you configure it to send updates by e-mail to a pseudo-address and to have "inbound mail" at that pseudo-address (on whatever target device) result in the execution of a local task, like, download task description file and import into Outlook? This would be a snap on UNIX/Linux because you can achieve it all through sendmail (the ilk, not necessarily the literal product) aliases, no need for special Office shims.
Is any of this making sense?