Compiling audacity to a separate directory

I have been unsuccessfully trying to get audacity to compile in a
directory different than the one that holds the source code. Audacity
always ends up complaining about the packages in lib-src not being
configured. For instance when I try

sanjoy@sanjoy:/tmp$ ~/new/audacity/configure

The configure script halts with the error

checking for WIDGETEXTRA… no
configure: error: lib-widget-extra is required to build audacity. A
copy is included in the audacity source distribution at

How do I rectify this? I really would like to keep my source tree
uncluttered …

The simple solution; make a copy of the source tree and compile it there.

That approach quickly gets out of hand once one starts incrementally editing the source code - making a small change in one file should not require copying an entire directory over.

A better solution would be to hack up a shell script / Makefile which copies files intelligently, based on the last modification dates. But creating such a script / Makefile will probably not be trivial (or so I think).