Just to clarify some points that are important. "Also, a tertiary halide with a bad leaving group cannot undergo sn2"... A halide is an excellent leaving group, the problem is that it won't undergo SN2 because of its halide attachment to a carbon to three other carbons. I is the most ideal leaving group for SN2, in order to do a SN2 reaction, the Halide must be on a primary or methyl group to continue.
The reason why you can't put it on a bycyclo compound is because of the tertiary compound. You might be able to do a SN2 on another source of compound, but that is pushing it... Especially since it is tertiary, thus, you must look for the nucleophile, if it is strong or not.
Make sure you read up on the criteria about SN2 vs E2's!