Creating a copy of a BISM Tabular project

Using Visual Studio to author SSAS Multidimensional projects, I was used to copy the project, deploy it with another name and then proceed with updates, until I was satisfied with the final result. Then, working with the two projects side-by-side I could check performance and numbers.

I tried the same technique with Visual Studio 2010 with CTP3 Denali with a Tabular model. I created a copy of an existing project but, as soon as I opened it, I got the error "This model is already open in another location by the same user, please close the other project before working on this one":