For our clients, we use the Workman's Compensation Maintenance to create codes for each L&I rate and enter the whole amount for the rate. This will debit an L&I Tax expense account and credit an L&I Tax liability account. The deduction from the employee check is an option for the employer. For those that do deduct from the employees check, we use a regular voluntary deduction as shown by @DebbieBeach, but we have it reduce the employers L&I Tax expense instead of add to the liability. Results are basically the same.
The workman's comp code is adjustable by earnings line so it works well for people who work in more than one L&I category, especially if they don't deduct from the employee's check. There is no built in way to marry the voluntary deduction codes to a WC code so the employee's portion has to be handled manually if the employee works in more than one L&I category.
Because the WC code is set on each line in payroll data entry, if it is set accurately, the employer liability is going to be accurate. If someone doesn't handle the voluntary deductions correctly, it only affects the employers expense.