Optimize should work as it will scale to give you a specific amount of bleed.
If you want to scale by percentage you can use the resize component. Resize the bleed box, make sure to not resize any other PDF box and make sure to scale the content.
Is there a way to add bleed consistently by scaling the page 101.5% using the resize component, then either using the Pressmarks or Imposition component to add crops? I get a lot of 8.5x11 documents by clients and would like to run it through a hotfolder quick to add bleed. The trim box size is usually 8.5x11 but the media box size can vary.