Hey @knircky
The best way to share post rewards with other beneficiaries is to use the chrome extension SteemPlus. It works for Steemit, Busy and Utopian as well.

You can download the extension here -
https://steemit.com/steem/@steem-plus/steemplus-extension-now-available-on-chrome-opera-and-firefox
It works for google chrome, Opera and Firefox so you can basically use it anywhere.

After downloading and installing the extension, you'll need to allow it gain access via steemconnect.

Adding beneficiaries for each post after that is pretty simple.

• Write your article as you would normally do, include the title, body and tags.

• Once you're done, instead of click Post, click on "Add Beneficiaries" under the Preview zone:

• You can add as many beneficiaries as you want as long as the total percentage doesn't exceed 95%.
  Your share of your own post will be 100% minus total percentage of other beneficiaries minus a small 5% share for SteemPlus.

This is the best service I could find. I believe it provides just what you need. Although they take 5%, I think it's worth the service they provide.
They also have a discord channel for steemplus incase you have any questions.
https://discord.gg/vKtTFg

Speaking of discord, I think steem-bounty should have a discord server as well. Users are growing quite fast.