Is it appropriate to use an Independent Study as a mechanism to get projects built?
Universities and individual departments have criteria for allowable independent study courses. One of the reasons is exactly the scenario you outline. In my department, approval will depend on whether there is "academic value" for the student. Academic value, however, is subject to interpretation.

By all means, inquire with colleagues, department chair, etc. to find out the relevant criteria for you. Of course the student should feel that the project is worthwhile for them, or you won't get anyone signing up. Students will prefer paid positions, all else equal. As you know, it is routine at research universities for students to be paid as researchers, to do the research that becomes part of their thesis. You have to offer more value, or accept a lower ability student.