SharePoint Designer Custom Action in Dialog

SharePoint designer has a great way to create custom actions. There are many help posts out there on how to do that.
http://blog.furuknap.net/adding-custom-actions-in-sharepoint-designer-2010
You have three options to select "Navigate to form", "Initiate workflow" and "Navigate to URL"
The trouble with these actions and options (well the ones on the View Ribbon) is that they do not open in the dialog box

There a heaps more posts on creating custom actions that open in dialogs
http://www.chakkaradeep.com/post/Using-the-SharePoint-2010-Modal-Dialog.aspx
http://www.vinodunny.com/blog/post/Application-Page-Ribbon-Dialogs-on-SharePoint-2010.aspx
http://jomit.blogspot.com/2009/12/dialog-platform-in-sharepoint-2010-how.html

The problem with those though, is that the action must be defined before hand.
I really like how sharepoint designer allows you to configure the url on the fly.
There must be a way to combine the two ways.

I was hoping that the "Navigate to URL" option would be a href.
So i tried a simple javascript:alert("hi") for an action.
Sure enough i got an alert box.
From there it was just a matter of figuring out the showModalDialog command, and putting it on one line.

This action is great to use with the StartWorkflow component http://spc3.codeplex.com/

For View Ribbon actions
javascript:SP.UI.ModalDialog.showModalDialog({url:"{SiteUrl}/_layouts/Com.CodePlex.SPC3/StartWorkflow.aspx?List={ListId}&ItemID={SelectedItemId}&Workflow=WorkflowName",dialogReturnValueCallback: function(dialogResult, returnValue) { SP.UI.ModalDialog.RefreshPage(SP.UI.DialogResult.OK) }})

And for Display Form Ribbon actions
{SiteUrl}/_layouts/Com.CodePlex.SPC3/StartWorkflow.aspx?List={ListId}&ItemID={ItemId}&Workflow=WorkflowName