In the past, I've had players e-mail me what their characters were doing during downtime. I then collated these and either posted them to a shared wiki or e-mailed them back out to the group. I did some editing as to what was public knowledge (what the team would know) versus what was private. I also conducted "intersession IC" this way, so that players could RP with NPCs or pursue private enterprises without bogging down the whole group.
I would award a point of karma if the player took the time to write up something nice and descriptive, say a couple hundred words. If they kept it short and basic (e.g. "Sir Derps-a-Lot is going to the shooting range this week to practice with his new Streetline Special") then that might not earn karma on its own, but if they showed consistency in their training over the course of a few weeks then that might eventually earn a karma discount when advancing the relevant skill or attribute. That's another way to keep an award specific rather than turning it into generic karma that could be used for any purpose. (It's also a way to slip some semi-covert discounts to the mundanes just in case they're falling behind the Awakened in terms of effectiveness.) We were running weekly so I didn't want to provide large karma awards, but if you're only running semi-monthly or monthly then you might feel comfortable awarding more than a point at a time.
Another tool I've used with great success is "knowledge karma". Namely, I'll give a separate karma award that is specifically intended to be spent on knowledge skills and contacts, which frequently go unloved in favor of higher-priority karma spending. The knowledge karma award is generally half the regular karma award, so a run or session that earns 6 karma might also earn 3 knowledge karma. Knowledge karma is another nice tool to have to reward blue booking, as it can often be used to make the character deeper or more interesting (or more useful, in terms of new contacts), but not necessarily more powerful. It can help satisfy the cravings of players who desire continual improvement without skewing the power balance of the game. It can also put a lid on the PCs who are constantly lobbying to turn every NPC into a contact (the noodle lady, the street urchin, the valet, ad infinitum), as you can deflect them with the appropriate price in knowledge karma. I use the same prices that are used for chargen, but I generally limit starting Loyalty to 1 unless the character has done something meaningful for the NPC, like rescuing them from a pack of horny ghouls. Wouldn't that be a bad way to go.