You can do that. It works when you get to scale and you're closing out early rounds. Remember that you need to create momentum and urgency to act!
You can call it a "Party Round" for small checks (<100k). You can say you are saving room for institutional investor who wants to put it more. If you need to, you can expand the round - "our advisory board has decided to extend the raise amount to $X to accommodate interest".
Make sure to to record the Zoom call and send it to anyone who can't come.
Position it - "we've decided on a syndicate / Party Round because we want a plurality of voices around the investor table. "
Wording to create urgency - "Alchemist has asked us to close the Party Round at a X valuation before we raise from larger funds and our valuation goes up. If you want to participate in this round, let me know."