I do not understand the exact result you expect but there are some options.
1) You can use a mesh fill, where you can not only change color of one node but the transparency itself. As the mesh can get complicated use a mesh of a simple rectangle and put it inside your shape.
2) Use a bitmap as the pattern you need as transparent.
3) Edit your gradient. For the case you mention "from bottom to top as well as top to bottom" simply choose linear and there is a cup icon on the properties bar. Clic on it and you now can choose several steps to that gradient. position and color. It is more complicated if you want diferent angles but it is a starting point.
4) Stalk objects with diferent blending modes. Probably some transparencies can be simulated this way.
Here are the examples and a hint of the configuration. All the shapes are still in vector and completly editable: