Although it'd be better if it did it natively, but I guess /a/ workaround could be to create a macro:

/macroicon "Enkindle Bahamut"
/ac "Enkindle Bahamut" <t>
/ac "Deathflare" <t>

Using Macro Icon will display exactly as "Enkindle Bahamut" does, including the cooldown timer so you know when it's available again. With Deathflare you don't need to know when it's available as it'll be available when you pop DWT so it doesn't matter if it still showed Enkindle Bahamut.

If Enkindle Bahamut doesn't work, it should use Deathflare instead. Though I've not tested the exact macro above, but I'm pretty sure it should work, as macros usually skip any lines it can't execute and move to the next one.