How to transform fermionic operators in qiskit

I encountered some problems when using the qiskit pakage to define the 2-electron reduced density matrix (2-RDM), which is a 4-index tensor, $$\langle a_i^\dagger a_j^\dagger a_k a_l\rangle$$. I need to first transform each term in the tensor (2-RDM) to the qubit form by Jordan-Wigner transformation. Then, I can measure each term using the expectation feature of the VQE function in qiskit. However, the qiskit.chemistry.fermionic_operator class only support Hamiltonian to be transformed to the qubit form. Therefore, there are two questions here to finish the 2-RDM measurement job. The first is how to define general fermionic operators by qiskit, especially the one has the form of the 2-RDM. The second is that are there any build-in function in qiskit to tranform general fermionic operators to the qubit form.