Ηere's a similar thread about a 386 compaq portable and win95 attempts on cga, in case you haven't seen it. Not that it worked though 😀
Upgrading Windows 3.1 to Windows 95 using CGA on Compaq Portable 386

Yes, it is possible.
640x200 in monochrome.
You have to make a driver disk using the Windows 3.0 drivers.

I remember reading a blog post where someone messed around a good bit with this and came to the conclusion that it could not be done. They did get the 3.0 drivers to work in a Chicago beta, but parts of basic system dialog boxes were cut off because the 640x200 viewport was too small. Windows 95s UI was designed around VGA, and in 640x480 some basic system Windows already fill the screen and so likely wouldn't even be usable under EGA. I guess you could track down a virtual desktop expander program, but the whole affair sounds painful. If you can get the 640x400 video mode to work, it might be usable, but "okay" and "cancel" boxes will probably be barely visible and you may have to set the task bar to auto-disappear.

I've also heard that the correct way to use the older drivers is to install 3.1x with the older driver, then upgrade in place to 95.

The Compaq perhaps supports that Olivetti M24/AT&T mono mode of 640x400..
You can check by running these simple test programs : Olivetti/Logabax/AT&T/Toshiba 640x400 hi-res graphics mode

If you're eager for experimentation, do a test installation of Windows 3.1 with a compatible driver.
And if it runs, let Windows 95 do an upgrade. Maybe it will keep that special driver in place.

The last Windows version shipped with CGA driver was 3.0, but such a driver was also provided for 3.1 - as part of the "Windows 3.1 Driver Library".
Maybe the driver for 3.1 was somehow updated, and has greater chances to run in 95 ?