Setting The Default Submit Button Without An Asp:panel?

I have a page with user controls getting dynamically added. Inside some of these user controls there are form elements, either simple <input> tags or complex third party controls (Telerik RadDatePicker for example) (technical details at end).

These controls are currently being identified as part of the same form based on a ValidationGroup string setting. My question is how can I get these form elements to submit on Enter together and raise the right postback event?

I cannot use the DefaultButton panel property because I don't have the id of the submit button available within the controls server-side. I think I might be able to use jquery clientside like this:

<input onKeyPress="javascript:if (event.keyCode == 13) {$(this).change(); $('#submitclientid').click();}" ...>

But I don't know how to do that for the third party controls.

Further technical details: Each form element is in a separate DNN module. Inter-module communication can be used to pass around data server side which results in multiple modules working together as part of a single logical form on a page.