I am sure you know how to add the predefined TextBox or ComboBox controls to a Windows Forms context Menu:

Just wanted to quickly show you how you can add your own custom controls to that context menu by using the ToolStripControlHost class, like this (the yellow panel is a user control):

Here is a short video:
And here is the code:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
namespace WindowsFormsApplication1
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
//instance my control
UserControl1 c = new UserControl1();
//pass as parameter to ToolStripControlHost instance
ToolStripControlHost host = new ToolStripControlHost(c);
//add ToolStripControlHost object to context menu. simple!
contextMenuStrip1.Items.Add(host);
}
}
}