Couple ways to do this:
Each time you export as OAM: You could break open the OAM widget by renaming it as a zip file, unzipping it, then optimizing those images, and then re-zipping it and changing the extension to OAM.
Or, one time, based on the current export state: When Hype exports images it will scale them down based on how your using the image in your document. So you would export to a folder on your desktop, optimize those files, and then go into the exported resource folder and manually replace every image. You would then need to turn off ‘automatically optimize when exporting’ – this would require that you add both the 1x and @2x version of each image back in. The first option is probably best 