Haha I've tried it before and yeah, hot water in a shaker doesn't work! Personally I would put some cold water in to shake up into a thick mix, then top up with boiling water in a mug.
Oh God no don't ever use the shaker with hot water, the first and last time I did that I doused the entire kitchen at work with shake walls and ceiling. It took my whole lunch break to clean up the mess.