You can add a series resistor to the gate. That's often done to slow rise-fall times in order to reduce EMI or prevent excessive overshoot. Obviously this increases switching losses (but not conduction losses), so there is a trade-off. As well as causing the switching to slow, it will also add a delay time, so keep that in mind if there is a chance of cross-conduction or similar problems.
The slope you get for a given value of gate resistor will depend on the capacitances from gate to source and gate to drain, as well as the value of Vcc. While the MOSFET is switching, the resistor supplies the current to charge \$C_{GS}\$ as well as the current to charge \$C_{DG}\$ between Vcc and 0. The total amount of charge is often specified in the datasheet (under given conditions) as the gate charge (measured in nanocoulombs). Because of the Miller capacitance (\$C_{DG}\$) the nature of the load comes into play as well.