Is it really not possible to use this add-on with XenForo 1.1?

This add-on can be installed and used with XenForo 1.1 without problems. However you need to modify your templates manually. The modifications can be taken from the XML file of this add-on, if you know what you are doing. Also the conditional for responsive view has to be deleted from this add-ons CSS template. If you do everything correct, the add-on will work with 1.1 also, however we cannot provide any support for this.