Technically, what you are looking for is possible to do, but there are a couple of "speed bumps" to watch out for.
1. myCRED it self will not allow log entries with zero points. This is because a lot of limitations in myCRED like maximum number of times you can do something each day are all based on your log entries. This means that we will need to update the database and add entries without using any of the myCRED provided functions.
2. You will need to keep an eye on limits you are enforcing since you are adding zero valued log entries. You might find some issue down. Just a heads up.
Now regarding the code.
You are correct in that we can use the mycred_add filter for this. But since we are not going to be able to use the add_to_log function we will need to populate the log our selves.
If you are comfortable with PHP, the mycred-functions.php file is the file that handles log entries and could serve you as a start off point. Have a look at around line 1011 where the add_to_log function begins. You could use this code yourself but remove the zero balance check.
Then it all comes down to checking if the user is over or under your daily limit and add entries into the log.
Let me know if you want some code examples.