C# .Net Entry, EntrySelect objects. How to add a checkbox field to a screen programmatically?

Hello,

I am trying to add a field to a screen programmatically. The problem is, the object of type checkbox is missing in SageCRM API.

Entry type property is readonly so the last line of my code below is irrelevant.

I also noticed EntryCustom object/class but it expects 2 parameters and i am not sure how to construct the second one.

EntrySelect comp_copy_to_opera = new EntrySelect("comp_copy_to_opera");
comp_copy_to_opera.OnChangeScript = "var tempVal = document.getElementById('comp_copy_to_opera').checked; setUpdateMod(tempVal);";
comp_copy_to_opera.EntryType = Sage.EntryTypes.CheckBox;

Any suggestions are very welcome.

Thank you.