Oh yeah course the yellow plastic bleeding spacer should suffice. Will give that a try, cheers.
(Hopefully won't be necessary but am quite surprised to learn from investigating it that if it were, replacement of the caliper seems relatively painless, both in cost and in job. Was thinking it might be several hundreds of pounds and the whole hose would need replacing, threading through the frame, PITA connection to the shifter, new olive, new special cutting tools, yada yada yada, but it seems it's only 40-odd quid and the hose just screws in at the caliper end.)