Many thanks to Ivy Alvarez and Mark Young, who both replied to my plea for advice on how to use diacritical marks in Blogger. Basically, it's plus the unicode or ASCII code number for the accented letter (see, for example, under the 'Insert symbol' menu in Word). You can either compile as you go or there's a list here.
I've done this now for the most recent one's on this blog. I will correct some previous posts when I can. I'm way too busy at the moment to go searching through the archives.