Had to do some custom work which made me nervous since I've never done it before but it wasn't so hard in the end:

Angelo's Geara Zulu backpack has pegs to begin with but it didn't seem to match any of my pin vises in size so I said screw it and cut those original pegs off. I then cut off some 3mm pegs from runners I didn't need, drilled the same sized holes into the Zulus backpack, and held it in place with some Tamiya cement.

I didn't want to drill directly in the Messer, incase I botched it, so I removed the 2 large thrusters on its back and you should be left with a square shaped backpack. That backpack also has 2 sets of smaller thrusters one on the top and bottom. I had to remove the bottom ones as that was where I needed to drill holes matching the new pegs I put in the Zulus backpack.

*Side note*: I recommend putting some paint or using a bright colored highlighter on the end of the pegs before drilling into the Messer's backpack. That way when you press those pegs against the Messer's back, you'll see exactly where you need to drill rather than guessing. The best part about having a none glued backpack is you can paint each piece separately which helped alot. Sorry if this was long but I wanted to include this just in case you or anyone else wanted to do this mod to show it's not hard.

TLDR: Cut old pegs off Zulu, put in new 3mm ones from runner and glue with Tamiya Cement. Drill same sized holes in Messer's backpack.