I did not read your original post carefully enough.
An example of one way you might handle this - assume CC Co contributes
1% of balance of monthly charges to the 529. You purchase a 'Widget' for $100 on your CC and you pay your CC balance from 'Checking'.
Create a category, e.g., 'Income:CC 529 Contribution' w/ no tax attribute assigned. Enter a CC payment transaction; $100 transfer to CC Acct. Add split entries; +$1 categorized to 'CC 529 Contribution' and -$1 transferred to '529 Acct'. Your CC is paid in full and the two $1 transactions offset.
The 'Income' will not be reported as taxable income in QW without a tax line assignment.
Not elegant but one way to get you there, I think!