a little batch file in the directory to execute "bin/geany.exe --config=portable_config" or something like this.
the idea was to avoid using a launcher to have the editor in portable mode, i know currently this is the only option.
Actually on Windows, Geany is binary relocatable.
For linux it may be worth adding another switch to override the `/usr/share/geany` hardcoded paths. This could make easier to run different versions of Geany witohut resorting to chrooted environments or similar tricks.