OK, info from OCLC suggests we need to find a non-PHP based solution:
To begin with, you can add whatever you like to the HTML pages. Though, there is no guarantee that they will work with EZproxy. Sadly, we do not provide PHP or HTML support, only EZproxy support. So, any changes that you make will not be something that we can/will assist with customizing.
There have been no development plans made for ILLiad to work on mobile devices. However, the ILLiad patron web pages out of the box should mostly work using mobile browsers, but they are not currently optimized for mobile access. Using the current web pages and the CSS files, a site with technical web developers could make these changes for themselves.