[danpat]

You always have the option of creating a map style and using Mapbox's Raster Tile API - although that does mean you probably can't dynamically adjust your raster images in time for a request to be served.

How are you using the Static Maps API currently where you would be able to send a POST request and display the image back to the user? Most use-cases for the Static Maps API involve the HTML <img> tag or something similar, which all send GET requests.