Void into solid from complex solids (NX10)

Hello,

I`m working with NX 10 and here`s just a quick question:

Is there any way how to convert "open" void (of a quite complex geometry) of multiple solids into a single solid? Also considering that the model one is working with is an imported from a .step-file.

As an example the following case (compared to the modell I`m working on, this one is actually rather easy one):

Any ideas appreciated.

Greetings

Eugen