Campaign Management - Chat Engagement Window

Hi all - within Campaign Management we are setting up a series of chat flows. We have customised our engagement windows and added welcome screens, however, the pre-determined 'fields' available for us to display on the welcome screen are somewhat limited/restricted to 8 fields.

My question is two fold - is it possible to add custom fields, and if so, how would I then enable them to display within this section for us to be able to collect this information from our customers at the welcome screen? I've dabbled with variables with limited success thus far.