As an 11B? If not what role do you think you could fill in Support or would want to fill for that matter. I am not questioning you (well I am indirectly), but what are you bringing to the table other than being able to close with and kill the enemy. There are plenty of positions you could fill supporting the ODA's, but I am not sure you are going to be all too excited about some of them. Something to think about...
As for your question, I am sure if the unit you are MOB'd with is willing to terminate your orders and demob you it is possible to IST to MOB with another unit. However, there is something else you might want to think about... The unit going to OIF, you volunteered to MOB with, is counting on you now. You have an obligation to them.
I would be sure to have all my ducks in a row when you call the SF SGM.
Sorry I couldnt be more help.
Crip