crowd

Hello, Is there a way to compile a php script so it won't be as clear text on the server ? The thing is that i have some company which want me to program some web application for them. They want to pay by license (by number of workstations which are allowed to access to the server at the same time). They are installing the script on thier server so i can't play with the server configuration. The only way i thought about doing so is by limiting the number of workstation by PHP commands in the script. so i nee to vimpile the script so they won't be able to  change it. I know there are some php scripts which are compiled out there (such as Pesk) but i couldn't find any tool/application to do so.