aftermarket carbon canister?!?! man what will they think of next...
venting to atmosphere = bad idea, you can get done for it, and also you don't want petrol fumes hanging around
theres a reason they use petrol in cars, and thats cause the fumes blow up real easy....
if i were you i would just relocate the stock canister if its that much of a drama, its only got rubber pipes attached, you can just move it anywhere you like really...