I'm in the same boat as you. I applied to McCombs as an external, but I didn't get in and so I'm in COLA as an Econ major. I'm hoping to transfer to McCombs internally and also going for a BBA in Finance. I'm going to try and get both a BS in Econ and a BBA in Finance. I talked to an advisor at orientation and they said that it would at most tack on an extra semester, so that's my suggestion.