Widget API for castbar

[MaLarsson]

I want to create a bar which shows how long the remaining time of a dot is.
I was thinking that you could use the blizzard castbar and pretend that the remaning time is a channeling spell.
What widget should I use for a castbar?
The one that stood out to me was StatusBar but it didn't have a method for setting remaning time like the cooldown widget has with Cooldown:SetCooldown(start, duration).
Is there a better widget to use for the castbar or do I manually need to update the duration of the StatusBar with StatusBar:SetValue(value)?