I don't think there's a way to do an actual floating VIP on the management interfaces. However, you can enable a management profile on another interface (such as your main inside LAN interface, or an interface you setup specifically for this purpose). You can then use this address to login to whichever device is active.
Is this just for ease of use for the GUI/CLI or for automation? If it's for automation, you can actually utilize the API call below to show the high-availability state result. Once you have the result it's just as simple as parsing the result to determine the peers HA state, and then you can pass your automation calls to the active peer.
If this isn't for automation and you simply want to have an easy way of only ever hitting the active unit, you don't have any other option outside of setting up an interface management profile as mentioned by @OwenFuller.
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