We have a similar requirement (Also in manufacturing) and have created generic users based on the skill type.
For instance we have a generic user of 'Designer' and a pool of users who also have the skill 'Designer'. This allows us to allocate the generic 'Designer' user to the task and carry the loading. The other aspect you then need to sort is that the generic user needs to have a capacity that matches all of those in the skill pool (5 users with skill, generic set as 500%).
It is not a perfect work around, but it is working for us, let me know if you want extra info.