Force Diplomacy on the other hand will work when they don't have the means to attack you.

Use move_character to whisk away offending enemy armies, send them to India or something and it'll be a long while before the Seleukids can gather big enough forces to trouble you again.

Course it helps if you're using the console to deplete their treasury as well.

Although if you're playing on VH campaign difficulty, you're screwed either way since they keep getting loads of money.