EDIT : Here the best solution : install it via npm : npm install -g slimerjs -g to be available everywhere. And that‘s it, juste choose your --engine=slimerjs with casper and it works. Thx for this node module.
For the best way to install phantomjs + casperjs + slimerjs without PATH and OS compatibility headlock :
npm install -g phantomjs npm install -g casperjs npm install -g slimerjs
In windows the exe will be set here : C:\Users\UserName\AppData\Roaming\npm (you don‘t need to put them in PATH, node -npm actually- manages it with the -g flag).
Keep in mind slimerjs has some relative path problems, so to keep the compatibility between phantom and slimer, use fs.workingDirectory, see Is there a way to step in to CasperJS code and Debug step by step