You may want to consider BR (Eva Air), a new member of *A, from SGN to either SFO/LAX/SEA/JFK (JFK requires long layover & transfers to EWR for IAH segment) and UA to IAH. Their award inventory will not be displaced on UA website. Do you have an UA office in SGN? Do you have a local phone number to book your award ticket? Here is one of the links regarding booking an award ticket on BR with UA miles,
http://boardingarea.com/onemileatati...n-eva-airways/