The standard JW justification for this is the Bible account of Rahab - she lied about hiding the Israelite spies, but was blessed by God for doing so.
IMHO, there are times when lying is justified - for the greater good, the lesser of 2 evils, etc.
JWs can and do exploit this for their own purposes of course - but so do lots of other organizations, religions included.
I.e., JWs are hypocrites, but I don't see them as being significantly more hypocritical in this area than some other groups.
Of course, then again, when you claim to be the only organization on earth with a direct pipeline to God, well, one would expect a tad more honesty than we get from them...