I don't think this is possible with a traditional Unix cron. It is possible there may be some version of some cron substitute software out there somewhere that has some kind of crontab-format extension to support this, but if so I am not aware of it.

My advice would be to just put the two lines right next to each other in the crontab file, with a single comment above them for both. Your crontab should be structured this way -- groups of related lines separated by whitespace -- in any case, for readability.