Recommendation Request and Academic Misconduct
If you are willing to strongly recommend the student for graduate study, despite his past cheating offense, then tell the student you are willing  to write the letter, and then write the letter.

Otherwise, tell the student you are unwilling to write the letter, and then don't.



Your edit clarifies that you are unwilling to write a strong recommendation letter, because of the student's past academic misconduct.  I suggest telling the student, "I am unwilling to write you a strong recommendation letter, because of your past academic misconduct."