The devs have been hard at work the last couple of weeks and an alpha version of CHDK for the Canon ELPH 300 HS and Canon IXUS 220 HS is now available on the CHDK forums.
For the latest as of right now, go to this post in the porting thread.
At the moment there are 2 versions for different firmware versions of the camera. You can check which you will need by using this software, along with a jpg you have taken with the camera.
If you are able and willing to test out this alpha build, please post your feedback on the CHDK forums to assist those who are developing. Also keep checking for new builds!
Check out my previous post for details on CHDK and its benefits.
Update: The builds are coming quick, this one is now the latest. Always check the thread for newer builds