That depends exactly why your printer, or your Mac, won't print that large file. It has to do with RAM in the printer or how OS X is sending the file to the printer.
In Windows, Windows stores large files and send parts of it to the printer when the printer can handle it. It is called Spooling. Mac should do the same.
But I have seen our office large format printer reject prints because they were to big. The only way around that was to add more RAM to the printer. Not sure if that is an option for your Epson printer.
Thanks for taking the time to reply. I have been in touch with Epson, who think that the problem lies within Lightroom and not with the printer. This morning I have done some adjustments to the page size in Page Setup and the cell size in the Print module. My mistake was to get the sequence wrong. I now specify the page size (Manage Custom Size) in Page Setup before I set the cell size in the Print module. This involves a bit of trial and error to get the proportions right in order to get the whole image to fill the whole of the paper, but this can easily be done by altering the image size/position in the Print module. (you could do it more efficiently by referencing the pixel length and width of the image and relating that to the cell/paper size). Many thanks for your suggestions and I hope this helps with your own large print issue.