Back to Mountain Electronics, Richard can program this driver: http://www.mtnelectronics.com/index.php?route=product/product&path=67&product_id=382 with up to 6 modes that you specify. You specify them as a percentage of maximum current and can specify the number of 7135s you want to set maximum current.
For example, the driver comes with 8x7135s 1x350ma + 7x380ms) as default giving approx 3 amps so you could ask for 2 of these to be removed to give 2.25A max current for your 1 minute burst, and then specify one mode as 22% to give around 500mA, and another mode at 27% to give around 600mA, and other modes to sort.
Of course you could have 3x7135s removed for 1.87A max and specifiy 27% and 32% modes for 500mA and 600mA respectively.
And it is called a moonlight special because the moonlight mode is what i believe you would call extreme firefly, which is another of your requirements met.
There are tolerances to consider so modes would only be roughly right not exactly right, but should be close enough. If you factor slightly lower than required you should get your runtimes with no visual difference in output.
Alternatively you may be up for programming your own modes, or even flashing a ROM with ramping software. I haven’t done it yet (have the electronics so soon!) so can’t help you with that but these threads would be the starting point: