I have... I used the same technique (same tip and hold it at the same angle) as if I were using royal icing. You'll just have to turn the cake to get all the petals on there. I don't have any pictures...I made them when I worked at a bakery and there was no time to make royal icing flowers. They are actually pretty eas to do!! 
Hey,
I just posted a pic I did with all buttercream flowers. The daisies aren't the greatest I've done, but you do the same technique as with royal icing. I believe it's tip #104. Just do it on a square and let it dry, it will transfer easy, just make a few extra. It's in my pics.
I do daisies in buttercream all the time! I use a flower nail and small square of wax paper. Then I use a 103 tip and w/the WIDE end out squeeze and pull in slightly and release pressure. Do them close together and make sure you are coming into the same point in the center each time! Pipe in the center using a small round tip and press down w/ sugar or edible glitter. Freeze (it doesn't take long) and take off immediately after removing from freezer and place on cake. You can use flower formers to curve,but depending how you put them on the cake they may not keep the curve! Set them against a side or rose etc. Anyway take out 1 or two at a time because they thaw quickly! You can let them dry but I don't always have that much time and this works great for me. Otherwise royal icing or fondant daisies are the alternative! Gook Luck and hope this helps!!
I made a cake with buttercream daisies and they turned out fine. I made them they same way, on squares of wax paper and let them set a little bit. Then I lifted them with the flower lifter-scissors and put them on the cake. There is a pic in the gallery.
HTH
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