I do the exact same thing.
I understand, some people have been doing this for a long time, blah blah blah.
But this whole extra stress thing.. have you noticed their hairs turning gray? They stop performing at work? Taking xanex? Just wondering.
I'm sorry, I know you probably weren't trying to order anybody to do anything, (hence the

) but I hear this a lot when It really has nothing to do with anything.
If feeding in the tank causes the snake to get substrate in his mouth, why not take them out? Sometimes changing substrate isn't an option (long shot, I know), and other times people just don't want to for looks, and would rather feed outside.
I mean, when I posted a video, I thought was fun, most of what I got was "Don't feed him in a seperate tank, and the food is too small". The food may be too small (kinda hard to judge at the pet shop), but feeding in a different tank is preference I would imagine.
Sure your snake may not eat when you take him out, but if it hasn't failed... don't stop. Even if it does fail 1 or 2 times, from what I've gathered, really has nothing to do with taking him out, but more along the lines of where he stays when he's not feeding.
I'm sorry I had to rant, but people correcting people on where they feed their snakes ALL THE TIME gets kinda old.
Sorry for the rant, I'm kinda new, but this seems to be one thing that gets said a bunch and sometimes doesn't need to be.
Back on Topic: Let us know how your snake does, it's sad to hear about a sad snake.