In Figure 1, the 12V is the Source pin of the P-channel MOSFET.If the Gate is low, the P-channel MOSFET is switched on.If the Drain is 12V, the Load is powered. But the Gate is still low and the Source is still 12V, keeping it switched on. To slowly switch the load on, the Gate voltage has to be lowered slowly from 12V to a lower voltage.Does that answer your question ?
For example with a resistor from Gate to Source to keep the Gate at 12V. If the Load is switched on slowly, the Gate should be slowly lowered from 12V to a lower voltage. Perhaps with a NPN-transistor with its collector to the Gate.
Sorry, I was thinking about schematics like this: http://circuit-zone.com/index.php?electronic_project=438
Using N-channel on high side would be possible if a voltage for the gate is available that is higher than the source or the drain. Like I wrote, that is almost never the case.