To smoothen the dt you could store the last n delta times and average them.
This could be done with an array, every tick push dt into the back of the array and if length is greater then n pop front.
To get the smooth dt loop over the array and add each stored value together, then divide it by array.length.
Interestingly there are engines like Godot that do delta time smoothing by default (can be disabled in the settings). Though their implementation is probably a bit better than what I am suggesting. This may be interesting for Scirra to consider adding to c3.