How can indirect jobs be used to fulfill an EB-5 direct job preservation deficit?

In a troubled business scenario, at least 10 full-time jobs will need to be preserved directly.

Only if you are a regional center, based on the number of investors, you should know the total number of jobs must be created/preserved. When you apply for a regional center, your economic report will indicate the total number of indirect jobs the project/business will generate. So long as the job preserved plus indirect jobs satisfy the requirement, you should be okay. But if you are a EB-5 direct investment, you cannot count indirect jobs. Your question is not very clear on who you are.

This depends on the regional center business plan. Most do include indirect jobs.

Indirect job creation can only be used in the regional center EB-5 project context.

If the I-526 petition is based upon a "troubled business," then indirect jobs may not be used, even if the new commercial enterprise was created by or is located in a regional center. Most likely, a new I-526 petition would need to be filed and the investor would start a new two-year conditional lawful permanent residence period. The removal of the condition in two years then could be based upon the indirect job creation methodology.

They cannot - it is only available to regional centers.

The only time that indirect jobs could be counted is if the EB-5 enterprise is through a designated regional center. When you are investing directly to a business, you could only count direct jobs created. If you invested in a failing business, then you need to save 10+ jobs from that business directly.