How to I change a file type in the WebIDE

I want to change the file type from .cpp to .c but the defaults are only .cpp and .h and the .ino file. Is there a trick to this?

I write in C, not in C++, (because I want to know exactly what is going on!). For the Spark I put the C in .cpp or .ino files. C is almost almost almost a subset of C++.