There are various strategies that can be used by someone with a job to avoid paying estimated taxes with respect to income not subject to withholding. Some strategies include:
However, be sure that the strategies you use address not only the income tax on your contract work but also any self-employment tax that may be owed.
IRA-type plan set up by an employer, rather than the employee. Salary-reduction contributions may be allowed to plans of small employers set up before 1997.