Perhaps write your own function to do this?
ie Create a variable (float) named updateRate and another (float) targetValue.
Create a function SetNewTargetValue (with two inputs NewValue(float) and Time(float)). Within the function, set
targetValue = newValue
updateRate = (NewValue-Currentvalue)/Time
In the Tick event, do this:
CurrentValue = min(CurrentValue+(updateRate*deltaDeconds), targetValue)
You will do the above only if (updateRate != 0 AND CurerntValue != targetValue)
I think this will give you a linear increase.