Not sure if its the same motor as my long canister vac n blo, but the layout of the canister is wrong to just stick another cover on the motor end with a tube, and find a filter that would fit in the shorter canister..
The 2 switchable motors in the Master Blaster are blowing out from the end of the canister where they are mounted to the tube at the other end of the canister..
A Vacuum has to suck air from the tube at the other end of the canister, through a (in my case), a long cloth bag, to hold the debris., and then through a foam filter, and out through the motor and the tube at that end of the canister..
The Master Blaster cannot do this, easily, I believe, without modifying or reversing the motors in the canister to suck air into them, through a bag, then through a filter, and then through the motors, and out the end of the canister with another tube there to exhaust the air..
Then when you want to use it to Blow, you have to change the set up again, Im thinking...
I get what you are wanting to do and Im sure that if it was possible to do this MetroVac would have probably invented the machine...
If you are in the New York area I believe that is where they are, perhaps you can go by their factory, or call them and ask them about this...
I am sure that they have been asked this a zillion times..
Good luck !
Dan F