You could create your custom validation attribute, like this:

[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field)]
public sealed class RequiredForPublishAttribute : ValidationAttribute
{
	const string defaultMessage = "{0} is a required property!";
	private bool IsDefaultMessage = true;
	
	public PropertyRequired()
	{
		
	}

	public PropertyRequired(string message)
	{            
		ErrorMessage = message;
		IsDefaultMessage = false;
	}

	
	public override bool IsValid(object value)
	{
		return !value.IsNull();
	}


	public override string FormatErrorMessage(string name)
	{
		return IsDefaultMessage ? string.Format(defaultMessage, name) : ErrorMessage;
	}
}

...then just replace [Required] with [RequiredForPublish].