Format Fields From SharePoint List in SSRS

Question

I've connected to a SharePoint list using SSRS with this query.

<Query>
   <SoapAction>http://schemas.microsoft.com/sharepoint/soap/GetListItems&lt;/SoapAction&gt;
   <Method Namespace="http://schemas.microsoft.com/sharepoint/soap/" Name="GetListItems">
      <Parameters>
         <Parameter Name="listName">
            <DefaultValue>{4AA7C92C-903F-44BE-A92D-0E3ECE89F74A}</DefaultValue>
         </Parameter>
      </Parameters>
   </Method>
   <ElementPath IgnoreNamespaces="True">*</ElementPath>
</Query>

I'm getting ssrs results formatted like this for a column that hold hours with two decimal places in the SP list.

string;#    // This is what is returned if the field is empty
float;#1.00000000000000   // This is what is returned for 1.00 in the list

How can I get this formated as a blank for the first case and 1.00 for the second?

PS I've tried setting the format code field in properties to "##.00" and it doesn't do anything

================================================================= EDIT

This almost works - it formats the numbers properly,

=IIF(Fields!ows_Non_P_S_Hours.Value="string;#","",
CDbl(right(Fields!ows_Non_P_S_Hours.Value,len(Fields!ows_Non_P_S_Hours.Value)-7)))

but for the null fields I get "#Error"