There's no such thing at the present time, and it's probably not easy to implement either, as wxExecute doesn't provide a means to control the process priority.
You can work around it if you must, by running your program as post-build step like this:
cmd /c start /belownormal yourprogram.exe
It may be possible to build this functionality into consolerunner by having consolerunner change its own priorty before starting the process, however this won't work with GUI programs then, as these are launched by Code::Blocks directly.