You have other options than making HUD SOI, but they're all more of a bother than it is to make HUD SOI I'm afraid. With the TGP I just pre-set the zoom to what will be an approximate level of zoom; I've after all already seen what there is to see when I made the Markpoint by and large. Re Mavs: If you set one of the MFDs to MAV when HUD is SOI, MAV it'll instantly become SOI if you press Coolie Hat forward short.
The Up Front Controller has a Steerpoint rocker switch. I mapped my keyboard A and Z keys to this function. Also mapped the CDU Mode Sw to the X, S and D keys.