That means target it.
It means use it.
It means the customer should get something out of it.
It means demonstrating how their feedback impacted the result.
It means checking that the change you made had the effect you both wanted and none either of you really didn't want.
Empower them. Give them optionA and optionB, they tick a box in the software, It dials back and logs their vote. Could be a prototype add on, a storyboard, just a link to a web page. "Have your say"
Your leverage, is they get something back for spending their valuable time on you.
I wouldn't knock the help desk myself. At the very least top complaint / query will give you something to look at, because by definition it means they find it hard to use.
But if you really want to do something pro-active, then it's sales and marketing you want to lock up with. Just make sure they know you haven't done the work yet.

Have a look at SUS (Software Usability Score).