Occasionally, we want to include some extra parts along in a build to order WO.  (We only do build to order.)  This is for times when a customer wants an extra part as a spare.  How can we add these parts so that they are correctly picked?
 
If the parts are marked as Normal type, we can't even include them on a WO.  If they are marked as a subassembly w/o a BOM, then they aren't listed on the picklist.
 
Any suggestions?

I don't know the details about when you know you want to add additional parts, but one alternative might be to use features and options if you know by the time you enter your sales order (assuming you convert your sales order to a work order.)