How to get (back) zram for 23.03.4 and later?

I do not want to use zram-swap, because of crashing my system in my scenario. Which is following:
Having 128MB RAM, I need to update the built-in modems firmware. Which is a package of files, about 100MB.
Having found some openwrt-docs (still) about zram, my idea was, to use zram for /tmp only, and to upload the 100MB there, which should fit.
No go, as zram has been removed.
Using zram-swap hogs the CPU, after uploading about 80MB, and finally causes a reboot. Which is explainable: zram-swap finally decides to kick in, to compress the 80MB, requiring quite some RAM to store the compressed stuff. Where to get it, as uploading only stalled, still to continue ? The 99% CPU load for quite some time, to compress 80MB is an another hickup.
An "insane" programmer like me expects a much smoother compression process, in case /tmp is zram from very beginning.

zram-swap does not work for you in new versions 23.05.0 or something, I still do not understand

If the router has a usb port, mount a memory stick and use that.

I use a Linux laptop and in similar situations I start the sftp server on the laptop and mount the appropriate folder on the router using sshfs.