Is it possible ETC1S without lossy compression ?

[progsung]

Question about ETC1S encoding options

If I plan to apply additional compression (e.g. gzip) to the etc1s result file, are there any suitable encoding options? - For example, is there any way to completely disable lossy compression?

Of course, in the case of UASTC, such encoding would be possible, but I wonder if there is no way in ETC1S.

*If that's not possible,
I'd like to know a suitable encoding option for creating similar results from UASTC.
Noted, the image quality that I aimed for is ETC1S level quality. (without alpha, just BC1 alike)

Thanks for your hard work!