Multiple research requirements?

[Temphix]

I am having a little dabble with making my own mod, and one thing that would help alot would be giving a unit (or building, weapon, etc.) more that one required technology to work.

What I have been able to do so far is give a faction a unique unit by unlocking a hidden technology at game start. I cannot however give them upgrades of that unit when further research is unlocked. For example I give the Imperium a unique trooper, I can allow them and them alone to make it, and even start with one.
I can't however give them tier 2 and tier 3 versions without either allowing all factions access to the unit, or giving all three variations at the start of the game.

I don't know enough about xml coding to add more than one technology requirement in the unit's file, so if anyone knows how you can do that it would really help alot. If it is impossible with the code I will just have to make do with just tier 1 versions.