Hello Hollywierdos,
Try Matlacha on the road out to Pine Island. There is a municipal park on the left side of the road after the bridges. Overnight parking? I don't know. There are several business owned launch ramps on the right side of the road. The first is at a bait shop (D & D or D & W ??) on the right before the bridges. Parking overnight would be fine there with permission from the owner. The drawback is about a 3/4 mile motor to the Matlacha channel at the drawbridge. The other ramps at businesses in that area are "parking challenged".
If you want to launch off the outer side of the island at Bokeelia or off the St James City end of the island there are several choices also. In Bokeelia there is a Lee County ramp. Take Stringfellow to Baranackas. The launch ramp is on the left into a canal that will let you exit through Shell Cut into Charlotte Harbor on the outside of Pine Island. Easy motor in nice canals. St James City has several launch ramps that I have seen, but not used. They also put you into canals. Those canals lead to the York Island area of PI sound inside of Sannibel Island at the end of the Miserable Mile.
I'm sure there are others you could use.
I will be in Cape Coral in about 2 weeks. If you need more info perhaps I can be of assistance when I am there. Contact me via a PM if I can help.
Phil