How to set a dynamic Context Key with multiples values in a Modal Popup Extender

Hi all, i have been going completely crazy with this matter in this days:

Scenario: Textbox with a value that i need to use, gridview with customers data that i need to use, modalpopup inside template column in gridview, and i need to populate a series of txtbox within a panel with a customers data from the gridviews selected row.( the gridview its bound to a datatable, and the info of the customers that i need its on another datatable in the DB, so i need a field of the gridview and the value from the textbox to get the info that i need )

i already set the dynamic context key to a column from the gridview, but i ALSO need to pass on the value from the textbox to the webservice, but, if i change the contextKey type of the webservice and add another parameter there, i get error web service 500  (besides the little fact tat i dont know how to use the <%#Eval( "use 2 values instead of just one" )%>).

Im also having trouble finding the way to populate multiple textboxes inside the panel of the modalpopup; if a try to use a gridview, or another control different than a label, as a DynamicControlID, i get a "cant find modalpopupextender" error. (and yes i have tryed another ajax examples and they all worked.... with labels :P)

i found an example in:

 http://www.aspdotnetcodes.com/Ajax_ModalPopup_PostBack_GridView.aspx

that represents just what i need to do, but it uses a javascript function, and i honestly have no clue on how to implement it, and i would like to write my own code also.

here i put some of my code to try to explain better what i whant to do:

WebService

[System.Web.Services.WebMethodAttribute(), System.Web.Script.Services.ScriptMethodAttribute()]
    public static GridView GetDynamicContent(string contextKey) NEED TO PASS ON MORE THAN JUST A SINGLE PARAMETER (NEED 2)
    {
        //DATABASE LOGIC TO GET A CUSTOMERS INFO FOR WICH I NEED THE CONTEXTKEY VALUE
//AND ANOTHER VALUE FROM A TEXTBOX IN THE SAME PAGE
        
    }

 

cModalPopupExtender

c1:modalpopupextender id="ModalPopupExtender1" runat="server" dynamiccontrolid="label6"
                        dynamicservicemethod="GetDynamicContent" DynamicServicePath="WebService.asmx"
DynamicContextKey='<%#Eval("ID_Cliente") %>' <!--NEED TO PASS ON MORE THAN A SINGLE VALUE HERE-->
popupcontrolid="Panel1" targetcontrolid="LnkVerDetalles"></cc1:modalpopupextender>

 And last but not least, how can i use multiples dynamiccontrolid´s in order to fill all the textboxes with the desired data(i honestly clueless about this point in particular)

Ill be more than gratefull if there is anyone that can give me at least a hint here, i have been stuck at this point for over 3 days now. Pardon my lame english, it aint my native language.

 Tnks a millon

Leandro