If i'm right they work just like any addon mod and are meant to be used with the 'invisible' driver mod.
So open these objects' cfg files and add/replace
slot 0 0 0 0 0 0 1
compatible 0x00023100 1
You should be able to attach them to your car and move them with the wrench tool now.
If they still don't work check if your car has NOS slots in the _carname_main.cfg file in scripts folder.
The nos slots should be above extra slots and under the battery slot so if they don't have any nos slots add the following lines in there.
slot 0.090 -0.130 1.950 1.571 0.000 0.000 500 ; small_N2O_canister_01
attach 0x00043100 1 ; small NOS canisters
attach 0x00043100 1 ; small NOS canisters
attach 0x00043100 1 ; small NOS canisters
attach 0x00043100 1 ; small NOS canisters
This should make it work bra.