On the same project I needed the same functionality for the CheckBoxList control. Because CheckBoxList hold ListItem I couldn't access the InputAtributes property of the CheckBox.

After some googling I found this post by Evan Freeman that explains how to create a new custom control that renders the server side values into the html code.

In this way you gain server side and client side functionality on the same time.

This is the code for the new ChcekBoxList control:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Globalization;
using System.Security.Permissions;

namespace System.Web.UI.WebControls{
[AspNetHostingPermission(SecurityAction.InheritanceDemand,
Level = AspNetHostingPermissionLevel.Minimal),
AspNetHostingPermission(SecurityAction.LinkDemand,
Level = AspNetHostingPermissionLevel.Minimal),
ToolboxData("<{0}:WorkingCheckBoxList runat=\"server\" />")]
public class CheckBoxListWithClientValues : CheckBoxList
{
private CheckBox _controlToRepeat;
private bool _cachedIsEnabled;
private bool _cachedRegisterEnabled;

public CheckBoxListWithClientValues()
{
    this._controlToRepeat = new CheckBox();
    this._controlToRepeat.EnableViewState = false;
    this._controlToRepeat.ID = "0";
    this.Controls.Add(this._controlToRepeat);
}         

protected override void RenderItem(ListItemType itemType,
    int repeatIndex,
    RepeatInfo repeatInfo,
    System.Web.UI.HtmlTextWriter writer)
{   
    if (repeatIndex == 0)
    {     
        this._cachedIsEnabled = base.IsEnabled;
        this._cachedRegisterEnabled = ((this.Page != null) && base.IsEnabled);
    }               

    ListItem item = this.Items[repeatIndex];
    this._controlToRepeat.Attributes.Clear();

    if (item.Attributes.Count > 0) //has attributes  
    {       
        foreach (string str in item.Attributes.Keys)
        {          
            this._controlToRepeat.Attributes[str] = item.Attributes[str];
        } 
    }
    this._controlToRepeat.ID = repeatIndex.ToString(NumberFormatInfo.InvariantInfo);
    this._controlToRepeat.Text = item.Text;  
    this._controlToRepeat.Checked = item.Selected;
    this._controlToRepeat.EnableViewState = true;
    this._controlToRepeat.Enabled = this._cachedIsEnabled && item.Enabled;
    this._controlToRepeat.InputAttributes.Add("value", item.Value); //add the value attribute to be rendered
    this._controlToRepeat.RenderControl(writer);
}
}
}

And thanks for Evan for posting this code.

Happy coding.

Netanel.