You might have been able to store the opcodes in strings, letting BASIC put them in memory somewhere and then getting the address.

A cool trick to move your player/missile graphics vertically in BASIC was to store the sprites in strings, point the sprite's starting memory to the address of the string, and then use string-copying routines in BASIC to move the sprite up & down (since they only had a horizontal-position register; vertically they were as tall as the screen, so you had to blit them to get vertical movement).

Yes, I learned that trick out-of the blue book, de re Atari I believe. Hard to remember.

I also used that trick to scroll one of the lower resolution graphics screns for a brick out type game that would inch whatever was left toward the player.