Assuming the following routing:
FUK-HKG-BKK-HKG-NRT-DFW-RIO, you will travel 16,863 miles. However, only HKG-NRT-DFW-RIO can be done on AA flight numbers (others on CX), so that is 13,496 miles.
L class earns AA qpoints at a rate of 1 per mile flown, so that is 13,496 qpoints. That is more than the 10,000 qpoints requried for the plat challenge.
Just make sure you book the AA codeshare on the HKG-NRT segment.