How to get a Humanoid to walk on top of a sphere?

I have a giant sphere, made out of triangles, which is supposed to represent a planet. I negated the default ROBLOX gravity, pulling the character downwards using a BodyForce object and used a BodyPosition (with some math, which gets updated every frame) to make artificial gravity for the planet. I also put a BodyGyro inside the Torso to make the character rotate accordingly.

So far, all the gravity problems are solved. However, when a Humanoid character tries to walk on a surface, that is too 'crooked' (upside-down for example, like on my planet), about 30 deg, the Humanoid's legs fall through the surface and the character is unable to move.

So is there any solution to this, other than creating a custom character system?