Conditional Required Attribute For Validation?

We're trying to get a conditional attribute to work, case in point, there's a boolean (checkbox) that if checked, its related text is required. So, ideally we'd have something like ...

public bool Provision { get; set; }

[ConditionalRequirement(IsNeededWhenTrue = Provision)]
public string ProvisionText { get; set; }

Is this even possible?

Alternate idea (not as elegant?)
public bool Provision2 { get; set; }
[PropertyRequired(RequiredBooleanPropertyName = "Provision2")]
public string Provision2Text { get; set; }

I'd hate to use the magic string method .