@adl Probably a better idea is to use a behavioral resistor instead of a B source, and that gives you what you need. Since you “legally” committed, now you have to switch to QSPICE 
The same technique to avoid using a constant current source as an output load (VERY bad idea): you can use a behavioral resistor instead of a constant source.
You could get theoretically PURE CONSTANT power (and not limited) if you replace the expression I={power}/{Vcc} with I={power}/abs(V(Vcc)), unfortunately that gives you infinity current when the voltage is zero, highly unrealistic. But, if for some reason you need that PURE CONSTANT power and you do not have zero input voltage, go for it! Although, better use something like I={power}/(abs(V(Vcc))+1m) to avoid divide by zero.
