You can’t do this, even if you’re subscribed. You have access to additional levels, but they are still locked behind the normal gate (getting 90% of kanji to Guru on a level).
A couple months is very little time in the grand scheme of things. Here’s a post from an advanced learner who used WaniKani (despite having already passed N1) and found value from it. And in their case it took them about 10 months to get to levels where most of the content was new.