Not as hard as it looks
Drill your first shafts well on the side. Without reshaping the whole thing, it cannot vent there.
However if it is too close to the "pop", this won't work. But until a few hundred cubic km have been removed, avoiding triggering it probably is better than speed..
Cheers,
Ben
"Career politicians are inherently untrustworthy; if it spends its life buzzing around the outhouse, it\ufffds probably a fly."
- [link|http://www.nationalinterest.org/issues/58/Mead.html|Walter Mead]