I had a few bits of hawthorn from a hedge sort out last spring, nothing as big as 8". When finished its rather nice, creamy white colour. I did a couple of small peanut serving bowls straight away and 'got away with it' without splitting.
Turned it green, only a couple of days after cutting, to a bit above finished size and wall thickness. Microwave seasoned then finished. During microwaving it distorted like crazy but didn't split.
My microwave method goes like this:
Weigh it.
Put in MW with a piece of kitchen roll loosely wrapped
c.90 seconds on medium or low power
Take it out, unwrap and give it a few minutes for the water vapour to go
Weigh, repeat .... etc.
After about 4 goes it stops losing significant weight, you're done ) I doubt it ever stops losing weight altogether but you sort of know when its right.
Back on lathe and finish. Expect the tennon or recess to be oval by now - you might need imaginative mounting solutions
Not sure if you could do similar for pens, maybe cut something over length and see waht happens of you hurry it up in the MW.