I've done that quite a bit but not with the p800. You might have to hold the paper just so to get it started due to the curl, but once the printer takes hold of the paper it should feed ok. Roll paper can curl up a lot but if you wrap it the opposite way around a 4-5 inch roll of paper towels and band it in place over night, it will straighten out pretty well. You need to tell the printer the size of the sheet prior to printing (USER). I usually include a little extra (over what I tell the printer) and then trim the ends after printing.
You can also buy precut panoramic sheet from some suppliers:
https://www.redrivercatalog.com/browse/panoramic-inkjet-papers-big-sheets.html
and roll paper
https://www.redrivercatalog.com/browse/roll-inkjet-photo-paper.html