For regions with net in-commuting (more income earned by workers who work in the area and live elsewhere than vice-versa), the net in-commuting rate can be found by navigating to Explore>Social Accounts>IxC Social Accounting Matrix and taking the ratio of Employee Compensation (EC) column payments to Domestic Trade row to the total of the EC column. For regions that are net out-commuting, this value will be 0.
The equation below allows you to adjust IMPLAN's estimated regional commuting rate to your known regional commuting rate.
newEC = EC*[(1-userCR)/(1-samCR)]
EC = original, unmodified employee compensation
userCR = your known commuting rate
samCR = commuting rate reported in the SAM
newEC = the EC value you want to use when running the analysis
For example, if the SAM shows that the average commuting rate in your region is 10% but you know that for your industry it is 20%, then: new EC = $1,000,000*(0.8/0.9) = $1,000,000*(0.88888) = $888,888.
After the scenario has been run, add the difference (EC - newEC) back to your direct EC effect since by definition EC occurs at the site of employment. Since EC is a component of Value Added, you should update the calculation of Value Added to include the difference. This way you correctly account for the in-commuters' direct effect, but you have also made sure that they did not generate any further local impact.