The only real problem with pushing the elements on the stack is that it's not really a viable option on the 6502, not on the system stack at least, and especially not string values. You can push them on A stack (Forth uses the top of Zero page and indexes with X), but that's using X as your stack pointer, vs the systems. You also still have the problem with stack scarcity for something large like a string.

You could still use the stack if you just push addresses (address of the pattern string, address of the list of arguments (which can be 2 byte integers, or pointers), and the address of the destination buffer).

I think the 6502 stacks treatise will be very helpful, especially the following chapters (although it's good to read it all, in order):

5. stack addressing
6. passing parameters
7. inlined data
13. synthesizing 65816 stack instructions
14. local variables and environments