I'm a mapper silly! No I'm not making illigal cs:s maps, however, I am working on a cs:s map that I will release AFTER the sdk is out and custom maps are legal.
The only way you could do it (without using the editor from the stolen build, which you're obviously not, being the upstanding community member that you obviously are) is to find that entity, create a new entry for it in the FGD for Hammer, and try and guess some key values.
Alternatively, just use func_breakable like you would for HL glass, and replace it when you import your map file into the new Hammer after the SDK is released.
Thank you Pi! It warms my heart knowing you think I'm an upstanding member of this community. You'll love my map, and I think I'll dedicate a piece of glass to you.
Chances are its one of the "hav..."s in the CS:S shared content.gcf/cstrike/materials/skyboxes, there are quite a few in there though, havbk, havdn, havft, havlf, havrt, havup.
Im pretty sure its all the directions, so back, down, front, left, right, up.