Mounting the stem in such a way that it doesn't extend well (at least 1-5") below the headset is very risky. Your steerer tube is threaded, and I'm surprised that there's enough thread to have an extra 2', but assuming there is, your dealing with a tube with 24 stress risers per inch. Your best bet is to trim most of all the excess tube off so the headset can be fitted as designed with no more than 1/2-3/4" max. spacers under the lock nut, and the stem inserted so it ends 2" below the lower cup (and also below the last thread).
If there's so much thread that there's still enough thread under the headset that the stem ends in the threads, it's still not good. The steerer will fail at the thread aligned with the base of the stem, but the deeper this is, the longer it'll take.
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.