I've just graduated with a BEng in Aircraft Engineering (Distinction), and I'm planning on completing 50% of the required modules for the Honours by the start of IOT, before picking up the last two in January 2015 (hopefully), as I can't see there being any real free time what with Phase 1/2 training prior to then.
There are plenty of distance-learning degrees but, if you're especially keen on Aerospace/Aeronautics, I'd suggest making sure (obviously) that:
The degree is accredited (RAeS, other authorised industry body form EngConUK)
Many part time engineering degrees can be very, very long (e.g. six years part-time).
If, unfortunately, you're unsuccessful perhaps look at completing an Ordinary Degree and then bumping it up to Honours, or completing the entire degree, prior to attempting service again?