Jan Jo,
The use of the temp tiddlers is hard coded in the plugin, but you could take steps to stop these temp tiddlers being saved to the file/server. See here
Perhaps @well-noted can provide a local storage mechanisium to look/save first to local storage, then look there first, if missing, then look for the temp tiddlers, with an option to disable/also save to the temp tiddlers.
If you are going to add these api keys to multiple wikis you could make a smart bookmarklet to install them into local storage over any desired wiki.