Yeah, you'd need to do it as a mod, either spirit (which has a lot of other features that are handy) or some other custom code.
http://www.goannasvencoop.com/sphinx/FTP/mods/spirit_of_half-life/1.5a4 is the latest official build with source code, and 1.8 is the latest offical build.
I'd suggest 1.5a4, however, because 1.8 has ugly random sparks everywhere fsr. 1.6 and 1.7 are made by a different team, and change the gameplay quite a bit, messing around with weapons and such. Plus they broke sitting scientists, which work in 1.5a4.