Applying for an F Visa in HK

I am a US citizen, normally resident in the UK, and I will be leaving soon to travel across SE Asia for 5 months before heading to China in April on an educational trip for 3 months. I have the invitation letter from the school and will be trying to get an F type - will I be able to get this in Hong Kong as I have been advised I cannot apply for one here more than 3 months in advance so won't be in the UK when this happens. Help!