I guess you are trying to enable some logic only on a certain condition, classical methods in my opinion would be a far more suitable option, such as using reset pins of IC's, gating signals (with and gates, although asynchronous methods would make most digital engineers shudder) or by doing proper synchronous logic with some kind of idle state or synchronous gating.
Anyway, not sure how to do such a thing, Proteus naturally infers any hidden VCC pin of an IC as power net and I am not sure how to change that. It's the common way, in every design I have worked on, all the IC's are hooked up to their respective rails at all times and control signals are used to determine if other IC's are enabled or not.
If you still wish to go this route and are interested in PCB design rather than simulation in ISIS, create your own symbols to match your needs, or place your relay contacts between power terminals. A specific VCC net for your logic IC, and VCC. In real life, the rails will not exhibit their respective voltages and hence do not need worrying about.