Back before the IT Nazis took over the PC's at my company, I loaded Cakewalk Pro Audio 9 and did all kinds of midi programming with the mouse - drums, keys, strings, etc. They don't care if we work with headphones on, so I could hear what I was doing in anonymity and save the midi file to a flopppy.
Now we can't load any software without admin priviledge, so I can only do lyrics in Word and email it home.
Also, if it's a rhythmic hook I come up with, I write it out. It takes forever for me but I've done it, and if I spend enough time figuring out the intervals, I can assign notes to it.