We would need a bit more information to resolve your problem because a sink drain does not always require a vertical vent line running above it.
Are your drain lines accessible from a basement or crawl space underneath?
What is the diameter and length of the pipe from the vertical riser in the wall out to the P-trap under the sink & the diameter and length of the horizontal line under the floor from the vertical riser to the Stack or Horizontal line it connects to?
Are you under the International Residential Code or the Uniform Plumbing Code as they both have some radically differing requirements for venting.
If you can provide a bit more information I may be able to provide you an illustrated layout.