Instead of copying the plug-ins into the XPE folder you can make XPE search for Photoshop compatible plug-ins in other folders on your disk. To do this click the plug-in icon (pictured right) and select 'Configure Plug-Ins Folder':
Click 'add folder' then browse to where your Photoshop compatible plug-ins are stored. If you have lots of plug-in in separate folders inside your top level folder, just point at the top level folder and the XPE will search for plug-ins in all the sub-folders. Repeat for as many folders as required, then click the OK button and XPE will install the plug-ins.
Some plug-ins may have been designed to work with a specific program, such as Photoshop. This means that the plug-in could have specific features that will not work in XPE. By default XPE will ignore such plug-ins, but you can override this option by selecting enable host specific plug-ins. Many host specific plug-ins work fine in XPE, so this way you can choose whether or not you wish to use them.
Once XPE has finished, clicking the plug-in icon (pictured right) will then present you with a list of available plug-ins. It will look like the following:

See also
Overview of plug-ins
Installing plug-ins
Using plug-ins