You could put a statement that sets the seed in the Extra template data field of each test case (a different seed each time). Then, use a per-test template (i.e. by unchecking the Is combinator checkbox) like
{{ TEST.extra}}
{{ STUDENT_ANSWER }}
This has the slight downside that any errors in the students code will have out-by-one line numbers, but students usually seem to get by. [It's possible to correct line numbers by post-processing but that's way harder.]