Really easy:

1.) Go to www.delta.com.
2.) Log in.
3.) Check availability and mileage requirements to HKG or BKK on DL flights.
4.) Abort when you see the actual mileage required for redemption in J.
5.) Book a different carrier (like I did using CO miles on TG) into SGN or HAN, or
6.) Book any carrier you want to some nearby city outside of Vietnam, and
7.) Call DL to book VN from that city to either SGN or HAN on a mileage redemption, but make sure you are sitting down when they tell you the mileage required for very short flights within Vietnam.
8.) Or, go to www.vietnamairlines.com and book your flight very cheaply with them directly instead.
9.) Roll on the floor laughing out loud at how inane DL is for charging so many miles for an otherwise cheap VN ticket.
10.) Finally, roll on the floor laughing out loud at how inane some people are for using DL miles to book otherwise cheap VN tickets.

It's really, really simple.