It can certainly be done. You can set the LOS requirement can be added to mind probe, the alien psi-amp or the human psi-amp to do what you want. For humans, you can even have multiple psi-amps to establish tiers. Something like:
- t1: requires LOS, high TU cost;
- t2: requires LOS, low TU cost;
- t3: no LOS req, high TU cost;
- t4: no LOS req, low TU cost (ie the original!)
I've attached a mod for two tiers (t1: LOS required, fast, based on sectoids; t2: vanilla psi-amp, based on ethereals) that I worked on for the XAE before Piratez abducted me. Would be cool to see something like it go into the FMP.