Template expansion allows %\1
, %\2
, etc. to reuse answers to a prompt, so you might try this:
("c" "Class" entry (file "~/sydbox/personal/workflow/class.txt") "* TODO %^: Week %^ Lecture %^\n SCHEDULED: %^T\n ** TODO prepare for %\\1-%\\2-%\\3")
For entering dates, it should give you a calendar. From there you can use shift-arrow keys to select a date, or these commands.