SELECT ... JOIN On Two Databases In VWD (?)

My environment:
XP Home, VWD, SQLEXPRESS.
A purely local setting, no network, no remote servers.

I try to do a JOIN query between tables in the membership ASPNETDB.mdf and one table in a self created 3L_Daten.mdf.

After dragging the tables into the Query Design window and connecting them VWD creates this query (here I added the control declaration):

<asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:ConnectionStringAspNetDB %>"
            SelectCommand="SELECT aspnet_Users.UserName,
                                 aspnet_Membership.Password,
                                 aspnet_Membership.Email,
                                 aspnet_Membership.PasswordQuestion,
                                 aspnet_Membership.PasswordAnswer,
                                 aspnet_Membership.CreateDate,
                                 aspnet_Membership.LastLoginDate,
                                 aspnet_Roles.RoleName,
                                [D:VISUAL STUDIO 2005WEBSITES3L_V1APP_DATA3L_DATEN.MDF].dbo.Personendaten.Age,
                                [D:VISUAL STUDIO 2005WEBSITES3L_V1APP_DATA3L_DATEN.MDF].dbo.Personendaten.Sex,
                                [D:VISUAL STUDIO 2005WEBSITES3L_V1APP_DATA3L_DATEN.MDF].dbo.Personendaten.Area
                            FROM [D:VISUAL STUDIO 2005WEBSITES3L_V1APP_DATA3L_DATEN.MDF].dbo.Personendaten
                            INNER JOIN
                                aspnet_Users
                            ON
                                [D:VISUAL STUDIO 2005WEBSITES3L_V1APP_DATA3L_DATEN.MDF].dbo.Personendaten.User_ID = aspnet_Users.UserId
                            LEFT OUTER JOIN
                                aspnet_Roles
                            INNER JOIN
                                aspnet_UsersInRoles ON aspnet_Roles.RoleId = aspnet_UsersInRoles.RoleId
                            ON
                                aspnet_Users.UserId = aspnet_UsersInRoles.UserId
                            LEFT OUTER JOIN
                                aspnet_Membership
                            ON aspnet_Users.UserId = aspnet_Membership.UserId">
</asp:SqlDataSource>

THIS WORKS, BUT:

As you can see the database 3L_Daten.mdf is inserted with its full path, which is not feasible for deployment reasons.

My question: How can I address both databases purely by their database names ? Both have been created within VWD and lie under App_Data.

(I tried almost everything, I practiced with the SQL Server 2005 Management Studio Express Edition, I tried linked servers, all without success).

Thank you for your consideration.