Here is the simplest way to do it: for each race on the ballot, list “Skip the runoff” (or “Elect the highest scored candidate”) as a candidate. If “Skip the runoff” wins the STAR election, elect the runner-up instead (who is the highest-scored other candidate.)
One more way would be to allow a voter to cast a vote in the runoff that is proportional to their scores by checking a box on their ballot i.e. Candidate A gets 0.6 of a vote and Candidate B 0.4 votes if your scores for them were 6/10 and 4/10. This is STOR (Score Then Optional Runoff) and becomes Score when everyone checks the box.