I don't think you can launch a Web Dynpro transaction with a standard launch button, but you can embed a Web Dynpro application into a Personas screen as HTML content.
See some of the following discussions for more info:
http://scn.sap.com/thread/3429713
http://scn.sap.com/thread/3445271
http://scn.sap.com/thread/3427439
I haven't really experimented with HTML controls yet, so sorry I can't be of more help.