Gridview Hyperlink value. Need to pass to another page but not using QueryString.

On btnSearch_Click event I bind the gridview. First column "Name" is the hyperlink and the second column "UserID" value I need to pass to another page but NOT using Request.QueryString.
Here is the visual of bind datagrid:
Full Name........................User ID....................Header title.................
Joe, Doe ........................123456...................other cell values ..........
Jane, Doe........................78910.....................other cell values..........

The grid might contain a single row or hundreds of rows.
Based on the code below I'm getting hyperlink href="nextpage.aspx?id=y&userid=12345" and so on. However, I need the following:
a. Hide the userid value so the user just sees "nextpage.aspx?id=y"
b. Pass userid value to the next page when user clicks on the link.

Should I use session variable,  hidden fields or what? But how? Example please.

<asp:gridview ID="gvGetUser" AutoGenerateColumns="false"..../>
 <columns>
<asp:hyperlinkfield DataTextField="Name" HeaderText="Full Name" ItemStyle-HorizontalAlign="left" ControlStyle-CssClass="lnk" 
 DataNavigateUrlFields="UserID" DataNavigateUrlFormatString="nextpage.aspx?id=y&userid={0}"  />
<asp:boundfield DataField="UserID" HeaderText="User ID" />
....
</columns>
</asp:gridview>

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