WebApi Model binding w/ 2 different objects

I need to create an end point, but this endpoint can have multiple types of input, the form itself can change based on configs, so i was trying to create at least 2 objects as possible inputs.

Something like:

public class ParticipationsController : ApiController
{

 public HttpResponseMessage Post([FromBody]Models.SimpleParticipationModel sModel, [FromBody]Models.CompleteParticipationModel cModel)
    {
        if (!ModelState.IsValid) // this might not be this way here 
        {
            return Request.CreateResponse(HttpStatusCode.BadRequest);
        }

        return Request.CreateResponse(HttpStatusCode.OK, "Ok");
    }

My point is to avoid having multiple endpoints and change a lot of renderization in the page.

My objects contain DataAnotations to obey certain rules such as "Required" and "Range 0-X".

I also didn't what to have an object with all the properties, and only fulfill some of them.

Thanks in advance