...so using the following code won't displays my files content
Does that mean you want to allow other people to deploy code on the server which calls your code without revealing the PHP source? If so, then disabling highlight_file isn't going to help much. You also need to disable include, require, fopen, file_get_contents, the imap extension and several other things - which means they won't be able to access your code at all.
If you're letting other people whom you don't necessarily trust deploy code on your server then there are lots of things you need to do to isolate each account - it's not a trivial exercise and well beyond the scope of an answer here. But it's not really possible to allow access to a shared include file without providing access to the source code. Using encoded PHP solves some problems but introduces others. A better solution is to expose the functionality via a web or socket API (this solves the sharing problem but not the isolation problem).