Ability to set default phoneme lengths in the dictionary

This would be a useful feature because I find myself blending vowels and changing the phoneme durations a lot to get a specific pronunciation like dancing as /d ey ae n s ih ng/ or can’t as /k ey ae n cl/ with shortened /ey/. But it’s inconvenient to change the phoneme lengths manually every time the word appears so it would be great if you could just set the default phoneme lengths for a word.