A leafblower pushes air, it cannot compress it. They are high volume low pressure.
Even if the airflow is funneled the air would back up and slow down the fan blades.

I am almost finished with a 6mm flamethrower.
All steel, 1/4" QEV "relay" valve, 1/2 hole vortex, blowgun trigger, sleeved feed ...

First off, let me start by saying that I have never before made a "spud gun" of any kind, and that this post is very likely to reflect that. If I say or do something incredibly stupid, please cut me a little slack.

Now, what I'm essentially looking to make is a "Flamethrower" type of weapon for use ...