Supporting documentation for tourist visa?

I plan to apply for a 12 month, multiple-entry tourist L; however, when I looked on the website, I noticed that one of the following documents is required in addition to the general application: an invitation letter (either from a tourist group, individual, or institution) or a copy of a round trip flight and hotel reservation.

I will be working in Macau for 10 months, and I would like to visit the mainland on weekends / during my breaks. However, I do not have a set itinerary at this time (no hotels booked). Also, because my return flight is too far in advance, I cannot schedule a round-trip flight. I expect to visit mainland multiple times during my 10 months in Macau, but I am not sure how to document this when I apply for it.

In this situation what type of document would be best to include with my application? Would a copy of my flight to Macau and a letter from my employer detailing my contract be enough?

I'd greatly appreciate any advice you can give me on the matter. Thanks!