Blending terrain textures inside the same alpha map via code

Hey guys, I really need your help!

I would like to know if there's a way to blend terrain textures through the use of a script. I'll try to explain better: I'm working on a grid-based terrain editor, the user will drag his texture on the grid that in the end wil form the final alpha map for the terrain. Instead of having multiple textures and playing with texture splatting I will have just one big texture for the terrain. So, is there a way i can blend textures inside the same map? Considering that by default unity uses multiple textures with alpha adjustment, I really don't know if that's possible.