How to pass in a generic type using a variable working it out at runtime?

I wish to make a generic extension method :

public static IList<ValidationResult> ValidateMany<T>(this IValidator validator, IList objectsToValidate)
{
    var results = new List<ValidationResult>();
    foreach (var obj in objectsToValidate)
    {
        var validationResult = validator.Validate((T) obj);
        results.Add(validationResult);
    }
    return results;
}

I would like T to be passed in. That may seem easy by adding a template param, but then from the calling code I would like to do :

// calling code
var typeOfT = WorkOutTypeFromObjects(objectsToValidate);
var objectsToValidate = ...;
var results = validator.ValidateMany<typeOfT>(objectsToValidate);

the top line there is the critical part that is hard to get, I need some dynamic way of working out the type and passing it in the T param. Or is there a good alternative?