Need to Compare Two Generic Objects Using Greater Than or Less Than

Synopsis: I have a need to take two generic C# objects, and if they are numerical, compare them using either less than or greater than comparisons.

Problem: I can't figure out how to have my class implement IComparable as described in this post: Having to implement a generic less than and greater than operation. If that's not even the proper path to take, then I need to know that as well.

Background: I have implemented the RequiredIf ValidationAttribute found at A more complex custom validator but needed the > and < options in addition to an equals comparison.

Code (taken from A more complex custom validator, one-third down the page):

private bool IsRequired(object actualPropertyValue)
{
  switch (Comparison)
  {
    case Comparison.IsLessThan:
    case Comparison.IsLessThanOrEqualTo:
    case Comparison.IsGreaterThan:
    case Comparison.IsGreaterThanOrEqualTo:
      if (!Value.IsNumber())
      {
        throw new Exception("The selected comparison option is only applicable to numeric values");
      }
      break;
  }

  switch (Comparison)
  {
    case Comparison.IsNotEqualTo:
      return actualPropertyValue == null || !actualPropertyValue.Equals(Value);
    case Comparison.IsEqualTo:
      return actualPropertyValue != null && actualPropertyValue.Equals(Value);
    case Comparison.IsGreaterThan:
      // THIS LINE FAILS BECAUSE actualPropertyValue DOESN'T IMPLEMENT IComparable 
      return actualPropertyValue != null && (actualPropertyValue.CompareTo(Value) > 0); 
    /