I don't know about humanly possible, but is it possible for the 164 to do it....no it's not.
This statement is incorrect. The OP has already said both systems he intends to track are Motorola. Many of us have done this by putting bot sets of control channels in the bank and separating them by unlocked conventional frequencies.
However, having said that; there are other issues. If the OP wants to receive all TGs (such as with the bank open), fine. But if the OP wants to alpha tag the TGs and/or limit which TGs are received, then it depends largely on which TGs are used by each system being monitored. For example, if system A uses TG 00016 for "Sheriff Dispatch" and system B uses TG 00016 for "Transit 1"; there is no way to select one and not the other.
After running my scanners this way for several years, I recently separated two of the systems I had in the same bank. Although I use the exact same list of TGs for both "systems" (there were zero conflicts in that regard), this gave me more control over which site(s) I can receive from at any moment.
I must wonder WHY does the OP want to do this? Why not just use two banks so that alpha tagging and control of what you want to hear can be more robust?