Short answer: 2/3 of it.
Long answer: It's really easy to complete Delta modules 1 & 3 online by using The Distance Delta, which is a collaboration of The British Council and International House. Bell also has courses but I haven't heard amazing things about it. Module 1 requires a written test, which you can only do at the British Council in Seoul twice a year. Module 3 requires no test and you just submit your paper online.
The tricky part is Delta module 2 which requires observed teaching. I looked at all the angles and think it's basically impossible to do in Korea unless you actually work at the British Council. Your only option is to go abroad to do it, which will take you 4-8 weeks and most of the courses are in Europe.