Sixth form registration

My parents have booked a holiday for September next year for what would be the first two weeks of term, but that year I'll be in the upper sixth and will go back to school two weeks later than other years, so I won't be missing any actual lessons. However, my parents didn't realise when they booked the holiday that during those two weeks I would have to go into school to register as an upper sixth student. Are there any ways that I could possibly get around this? Do all sixth form students have to register on the same day or would I be able to do it at a later/earlier point?