I'd be happy if there was a way to do it either way.
A potential workaround that I've discovered is to set up an ifttt recipe to send you a text message at a certain time. You then might be able to set the custom vibration for ifttt if they in fact always send the text from the same number.
Basically, the reason that I want this functionality is so that I can keep my phone in my pocket and have it give a custom vibration at the top of the hour or at certain intervals so that I can generally keep track of what time it is without having to look. I wouldn't use this all the time, just during times at work when it would be impolite to be pulling out my phone to check the time.
The reason it would need to be a custom vibration is so it would be distinguishable from emails and texts.
Kind of an esoteric problem, I'll admit. But I was just curious if there was a simple solution available.