My method of attack would just be to paint it in with a regular brush, no pun intended.
Not sure how much paint you wanted (I went with a little bit more than the sample image -- gorgeous image by the way) or how big/globby you wanted the paint drops, but the nice thing about painting is you control every detail.
I would find a matching brush and matching red glossy paint and shoot them and the drips on the floor and composite the image together. Especially if your not an great artist or else can look real fake.
I'm also liking the composite image idea with reshooting the hand and paintbrush. If that's more convenient, that would definitely be another way to go. (Lack of photo equipment here means I'm forced to paint it in instead)
Peano's brush is probably the most realistic in this thread & Platinum Dust's drips/splatter are very very nice. I agree that a composite might be the best way to go unless you want an overly cartoony effect on an otherwise nice image.
There are several sets of paint drips and splatter brushes for Photoshop that have the shadows and shading and highlights built into the brushes themselves. They can be painted on ...and then Free Transform > Warped... or even better... Puppet Warped around the hand. You can pull the paint and bend and wrap these brushes around the hand with the transform tools.
Some of these paint splatter brushes are free (Google: Free photoshop paint and splatter brushes) and they obviously can be colored the same color as the dress. This might be an intermediate solution if you are not a freehand artist.
If you do this painting on a clear transparent layer above your image...you can make many trials and play around with it until you get it to look the way you like it.
Yes it will be some work...but then you will have a new skill as a result.