It's not currently possible, though Lewis Polk did say that they were going to look in to it.
Honestly, I've been using the radio for a bit, and I that once you get used to it, not seeing the timer isn't a big deal. I just set for a bit shorter than my fuel supply, and I know I should think about landing after it goes off. But I leave enough cushion that I don't need it down to the second.
I was using a seperate countdown timer, but I found I never really looked away from my plane in the air to look at the timer anyway, I just reacted to the noise it made. I mean, how much time do you spend not looking at your plane in the air anyway?
That said, I'm still not 100% confident that the timer is running or not running when I think it is. And, if I understand, it starts up automatically when you turn on your TX, while most guys prefer to start their timers right after the engine starts. You can stop and re-start the timer with the buttons on the pannel, but you get no feedback telling you that it's doing what you think it's doing, that it actually stopped and re-started. Some feedback here, even just a beep for "started timing", two for stopped timing or something would be an improvement. Though not necessary if they do the mod to make it visible.