I'm missing something?  I thought String.Format took custom format
strings...What about something as simple as:

   class Program
   {
       static string FuncTest(string format, object obj)
       {
           // Parameter check here - format not null, object not
null, object type valid, etc...
           string realFormatString = "{0:" + format + "}";
           return string.Format(realFormatString, obj);
       }

       static void Main(string[] args)
       {
           double MyPos = 19.95234, MyNeg = -19.9551325, MyZero =
0.0;

           // In the U.S. English culture, MyString has the value:
$19.95.
           string MyString = FuncTest("$#,##0.00;($#,##0.00);Zero",
MyPos);

           // In the U.S. English culture, MyString has the value:
($19.96).
           // The minus sign is omitted by default.
           MyString = FuncTest("$#,##0.00;($#,##0.00);Zero", MyNeg);

           // In the U.S. English culture, MyString has the value:
Zero.
           MyString = FuncTest("$#,##0.00;($#,##0.00);Zero", MyZero);

           int iMyPos = 19, iMyNeg = -19, iMyZero = 0;

           // In the U.S. English culture, MyString has the value:
$19.00.
           MyString = FuncTest("$#,##0.00;($#,##0.00);Zero", iMyPos);

           // In the U.S. English culture, MyString has the value:
($19.00).
           // The minus sign is omitted by default.
           MyString = FuncTest("$#,##0.00;($#,##0.00);Zero", iMyNeg);

           // In the U.S. English culture, MyString has the value:
Zero.
           MyString = FuncTest("$#,##0.00;($#,##0.00);Zero",
iMyZero);
       }
   }

[...]

Actually, there is... I posted it in my previous post. It was the entire
lower half.

Also, I wouldn't do what you were showing there, rather, just make the
method overloaded with different data types as the argument:

public string someWork(Int32 num)

public string someWork(double num)

public string someWork(float num)

public string someWork(Int64 num)

And so on.

Still, given you can format it in a custom fashion, I don't get why you
still think it's a problem. I gave you a working code example displaying
the fact that String.Format *DOES* support custom formatting.

Chris.