This has been discussed before, but I’m not aware of any solution.
Several WMS/WFS client applications present users with a list of available SRS determined from the capabilities document - if there are no alternatives listed, then only the default SRS is available.
Geoserver does NOT provide the list of supported SRS in the capabilities doc (which I think makes it non-compliant with the spec? eg: 7.2.4.6.7 of the WMS spec)
I’m aware of earlier discussions that including some 5000 CRS’s in every layer creates a bloated document & I agree in principle.
However, to solve one of the problems we have encountered in our migration fom mapserver to Geoserver, is it possible to allow Geoserver to advertise specified CRS’s in the capabilities document? So the admin menu lets some CRS’s be identified & selected to be so advertised. This would not preclude unadvertised CRS’s being supported as well, but I think does address this issue.
If this is considered viable, I have access to some funding which could pay for it to be implemented.