One other thought might be to buy a complete lower, which you shouldn't need a permit for, and then buy a seperate upper. Might be the easiest way to get one.
ETA
Never mind, I read the other thread. I do think the dealer you're buying from is an idiot, because it doesn't qualify as an assault rifle, since it is just a lower. The following is from the BCA website. the dealer can't say it's an assault weapon, since it doesn't have the features.
BUREAU OF CRIMINAL APPREHENSION
LIST OF FIREARMS INCLUDED WITHIN THE DEFINITION OF "SEMIAUTOMATIC MILITARY-STYLE ASSAULT WEAPON"
AUGUST 1, 2001
Pursuant to Minnesota Statutes 624.712, Subdivision 8, the following is the BCA's current authoritative list of the firearms included within the definition of "semiautomatic military-style assault weapon".
A firearm is considered to be a semiautomatic military-style assault weapon if it is:
Any of the firearms, or copies or duplicates of the firearms, in any caliber, known as:
Norinco, Mitchell and Poly Technologies Avtomat Kalashnikovs (all models),
Beretta AR-70 (SC 70)
Colt AR-15
FabriqueNationale FN-FAL, FN-LAR and FN-FNC,
Action Arms Israeli Military Industries UZI and Galil,
Intratec TEC-9, TEC-DC9
SWD M-10, M-11, M-11/9 and M-12,
Steyr AUG and
Revolving-cylinder shotguns such as or similar to Street Sweeper and Striker -12.
A semi-automatic rifle that has an ability to accept a detachable magazine and has at least two of the following:
Folding or telescoping stock,
Pistol grip that protrudes conspicuously beneath the action of the weapon,
Bayonet mount,
Flash suppressor or threaded barrel designed to accommodate a flash suppressor,
Grenade launcher.
A semi-automatic pistol that has an ability to accept a detachable magazine and has at least two of the following:
Ammunition magazine that attaches to the pistol side of the pistol grip,
Threaded barrel capable of accepting a barrel extended, flash suppressor, forward handgrip or silencer,
Shroud that is attached to or partially or completely encircles the barrel and permits the shooter to hold the firearm with the non-trigger hand without being burned,
Manufactured weight of 50 ounces or more when the pistol is unloaded,
Semi-automatic version of an automatic firearm.
A semi automatic shotgun that has at least two of the following:
Folding or telescoping stock,
Pistol grip that protrudes conspicuously beneath the action of the weapon,
Fixed magazine capacity in excess of five rounds,
Ability to accept a detachable magazine.