Is there any way to do this?

I have J. Martinez in LF and 2 even worse fielders platooning at DH. With a lead, I want to move Martinez to fill both DH slots and a good fielding LF to replace Martinez.

You can't move someone from the field to DH, nor can you move somebody from DH to the field. You can definitely put in a defensive sub for Martinez, but I understand you not wanting to lose any potential at bats.

You can't move someone from the field to DH, nor can you move somebody from DH to the field.

This is not a Strat rule, but actually it's a MLB rule.