Do you mean when your new growth makes your cornrows space apart?
If so, I think using a weaving net over your cornrows and then crocheting hair to the net will work. Like this:
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It's what I do when doing the "Lazy Girl" method for my crochet installs bc there is no cornrowed base. HTH!
ETA: If you're wanting to preserve your current install, I would think you could to the same thing with just a portion of weaving net by removing the crochet hair from your cornrows and then lay a cut portion of weaving net across the top. Then reattach the crochet hair through the net and your cornrows and fill in the gap areas by crocheting onto the net only. But I'm not sure if you think it's worth doing all of that just to preserve the style another week.