I would suggest creating a skin for the purpose of only being a spash page skin, and using it for that page.  Then, in that page, use the appropriate module to show your splash page content.  Finally, in the Page Settings for that page, add the following mark-up to the Page Header Tags field.

<meta http-equiv="refresh" content="5;url=http://www.somedomain.com/Home/TabId/32/Default.aspx">

Be sure to also specify your splash page in the Site Settings.

That will work as long as you do not need to utilize any of the DNN functionality on the splash page.  By not using the dnn page, you are not able to hand-off management of the page to an admin or any other content management group.  However, if you are the content management group, then this workaround will work fine. 

But keep in mind, you will need to revert to my original suggestion should you ever get anyone that will need to manage that page in the future (i.e., graphic designer, SEO, etc.),  Not doing so requires you to utilize a whole different set of permissions and permissions system (i.e., Windows).  It would no longer be an online management scenario, but rather an HTML, FTP, and Windows Permissions scenario.