You can add bailey's to the pudding powder/cream mousse... just may need to add a little extra powder to compensate
What about a white or dark chocolate baileys mousse. I have a recipe for it, if you need it. I actually make a crust and usually fill it with the mousse but it works well also for cake fillings. Just make sure to put down a layer of buttercream first so it doesn't absorb into the cake.
You could also do a soft chocolate ganache with a bailey's flavor to it.
Basic buttercream thinned out with bailey's would work also.
Here is one to look at, there is a frosting recipe there...
http://www.cakecentral.com/cake_recipe-3133-0-IRISH-CREME-CAKE-by-Paula-Deen.html
Here's one from Ladycakes.com - It's really good! she's got a ton of great recipes! http://www.ladycakes.com/Recipes/Fillings/Bailey's%20Chocolate%20Mousse%20Filling.htm
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