RadSpell does not offer such a facility. It is always a user action that triggers the popup and contacts the built-in handler. The closest available option is described here: http://www.telerik.com/support/kb/aspnet-ajax/spell/details/server-side-spellcheck-using-radspell.
Perhaps you can consider implementing a webservice call that will send the textbox contents to the server where the web service will handle the MS Word integration if it has suitable API that you can use. You may find this post helpful on calling the service: http://blogs.telerik.com/aspnet-ajax/posts/13-03-21/different-ways-to-make-a-request-to-the-server.
If you succeed in creating such an integartion I would encourage you to post it in the RadSpell code library section and we will gladly award your efforts with Telerik points: http://www.telerik.com/support/code-library/aspnet-ajax/spell.
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