Before you go to all that work, just rig up a quick Tee and see if it makes too much foam....THEN run your lines to the exterior once you know it works.
The only issue with a Tee, or with any fitting inline, is it creates a restriction in the line. the restriction causes an increase in superficial velocity and a decrease in pressure, (venturi effect). The decrease in pressure can cause CO2 to crash out of solution. Best defense against this is to get an oversized barb. Got 3/16" beer lines? Use a 1/4" Tee at least, and heat the tubing so you can stretch it over the barb. A larger barb will have a larger ID, reducing the venturi effect.