DataSource Controls :: How To Use A Property Of An Object In Asp:SessionParameter

I am trying to get an asp:SessionParameter of a SelectParameters, to use a property of an object in session
instead of having a string in the session like Session["CustomerID"]

Something like Session["Customer"] where the property is ((Customer) Session["Customer"]).CustomerID)

My code:

<asp:sqldatasource id="SqlDataSource1" runat="server" connectionstring="<%$ ConnectionStrings:DBConnectionString %>" xmlns:asp="#unknown"> SelectCommand="SELECT * FROM getStoreCustomers (@customerID,@week,@day)"
ProviderName="System.Data.SqlClient">
<selectparameters>
<asp:sessionparameter name="customerID" sessionfield="Customer" /> ?????? (what is the syntax to pass the property here?)
<asp:controlparameter controlid="ddWeek" defaultvalue="-1" name="week" propertyname="SelectedValue" /> <asp:controlparameter controlid="ddDay" defaultvalue="-1" name="day" propertyname="SelectedValue" /> </selectparameters>

The class I use is like any other class (but serializable)

[Serializable]
public class Customer
{
public int CustomerID
{
get;
set;
}
}