Enabling MTP in HTC Desire S My use case scenario is following: push some data from pc to smartphone and have an app there that detects and read that data. 
I know that there is MTP protocol that allows both pc and mobile device to access storage simultaneously. In that case I could just drop some files on mobile's sd card and have File Observer set to detect changes in file system and then subsequently read that data.

The problem is enabling MTP on HTC Desire S. I read that HTC Android 4.1+ versions support this protocol. I tried newest official ROM for the phone (4.0.4) but there was only Usb Mass Storage option when connecting to pc. Now I am on Jelly Fire Bean, 4.2.2 and still I can find no trace of MTP support. Might it be that this is a hardware limitation of the phone or have I not tried the correct ROM yet? 

Alternatively, is there any other way to fullfil my use case scenario? The constraint is that communication must go through the (USB?)cable.
An alternative would be to use adb push resp. adb pull to initiate a file transfer between computer and Android device. For this, you don't even need the entire Android SDK on your computer, a few files suffice (see: Is there a minimal installation of ADB?). On a Linux system, you could even mount the Android device using adbfs (see here), and thus access it like a "normal drive" from command line (e.g. via cp/mv) as well as from graphical interfaces.