On our annual bid forms there is a 50% and 75% option to take. not sure how it works - i.e 1 week on 1 week off or total flying to be X% of the pilots agreement.
I would guess that it would only be for current employees to take. I don't imagine them to want to take on DEP on a part-time contract (although if this is against EU regs I stand to be corrected)