HTC ONE & GOOGLE NOW Shortcut
GOOGLE SEARCH & GOOGLE NOW are basically the same thing,but,I think you're referring to a direct link to VOICE SEARCH.Seems the action you're describing was present on my phone @ one time,but,I can't get the long-press action to open directly to VOICE SEARCH anymore,but......
If you go to GOOGLE SEARCH,scroll down to the bottom of the page & press on the 3-dot icon,which opens up a menu,press SETTINGS > VOICE > & select "HOTWORD DETECTION".
Then,the next time you long press to open GOOGLE SEARCH,just speak the word "GOOGLE" & VOICE SEARCH will be open.
If you're using an aftermarket launcher such as APEX/HOLO/NOVA,you should be able to set-up a long-press profile for the home key to open up to just about any application or shortcut imaginable.