@Dismesquared
I know how it feels. Trust me. I am currently in my MBA program but I still know how it was for me when I needed the LOR from my supervisor who was also the owner of the organization. I was in the top hierarchy which is a way worse position to be in.
A lot of my clients face the same situation and it is perfectly normal to fear that it will sabotage your professional career.
You mustn't take the LOR from the Current colleague as it is a big no from any MBA consultant as it may not be perceived well by the admissions team.
I am happy to chat with you to find more options that you can use, but an LOR from Current supervisor displays- a. Commitment to an MBA degree and b. A reflection of your current status
There's a reason why those that produce their current supervisor as primary recommenders have an advantage in application process because they have been brave enough to take the risk.
Because the Adcom will ask a simple question when you say that you don't want to ask for the recommendation as it will sabotage your professional career (in the optional essay)- So do you think all these other people didn't face the same issue?
It will come off as less empathetic and it may hurt your chances of admissions so, I suggest finding a strong reason that will not backfire on you.
The admissions team is looking for opportunities to admit you (AND OTHERS). So, if you give them an opportunity to find a leadership flaw, they will use that to get another candidate in. Like I always say, MBA applications aren't a joke, every word matters.