I Want A Promotion But Don't Know If I'm Getting One. A Managerial Query.

So, for the past month I've been picking up serving/cocktailing shifts with more regularity. I haven't been given a set schedule of shifts, nor am I put on the weekly schedule emails. However, one of my server buddies told me I'm on the contact list, aka if you need a shift covered you can call me. Two weekends ago I worked on Saturday and Sunday night. This week I did a surprisingly busy Wednesday night shift.

Via text message, I am confirmed for working the dinner shift on Monday, Tuesday and Wednesday. A manager told me these are good opportunities to get my "high-volume skills up." I'm looking forward to the busier and more lucrative shifts, but as of yet I have no indication that those will be a regularly occurring phenomenon in my life. I've emailed and talked with management enough times to be 100% sure they know I want to be on the regular schedule. Do I have any recourse to make that happen? Other than taking whatever shifts I can get, I don't think so.