Wow, what a wacky question.
Once you got the gas block small enough so that the barrel nut could slide over it, what do you propose to do about the gas tube?
It's still going to be under the barrel nut when you get the barrel nut up close to the reciever.
Maybe you could just roll up the gas tube around your finger for a second while you slip the barrel nut on the threads.
Then you could just poke it into the front of the reciever and set it between a couple notches?
It's not like you would be able to turn the barrel nut with the gas tube in the way otherwise.
Have you ever pulled the handguards off your rifle?

Quoted: Why is that so crazy?

It's not crazy to want that, but it's also not possible to DO that.
The major limitations of the AR barrel nut is the barrel extension flange.
The barrel nut part of the handguard tube can not be much over 1.1" or there will be nothing holding the barrel extension flange against the receiver.
Making a gas block that fits around a 0.750" gas block that properly locates the front of the gas tube so that  regular tube can be used is just not physically possible.
Now, you COULD go to a 0.625" diameter barrel, a  specially bent gas tube that allows the block to put the front of the gas tube closer to the barrel while still going straight into the reciever/gas key.
What does this really gain you?

I have the perfect solution for your situation...
Yankee Hill specter gas block.



It clamps on to the barrel so there are no pins to remove.
If you want to remove the handguard, just remove the screws, slide out the gas block/gas tube assembly and unscrew the handguard.
No need to even knock out the gas tube pin.

How often do you plan to remove the barrel from the reciever anyways?

You might consider an MGI CQB or an LMT MRP if that's important to you.