It’s simple, run a designed route for the guy ffs lol. Take something you would’ve done with andrews or hurst, swap Boykin, and maybe adjust the play to get Boykin wider and more space to run if desired.
Beyond that, just diversify his tree some, stop making him a decoy, get him isolated on the boundary and design some back shoulder throws for him, and work some slants and seams with him as the first read.
Lamar clearly has his rapport with andrews and he seems to shy away from most others, design plays for Boykin and Lamar will begin looking his way more.