Usually I would say create a resource "Implementation Team" or "Developers" and set the maximum units over 100% to represent that you have more than one of those people with the appropriate skills.

However, you state that they cannot be assigned to the task at 100% -- that's fine, you can certainly assign at below 100%.

Another option is to create Developer1, Developer2, Developer3, etc. and set the max. units for each of those resources below 100%. The advantage of this method is the resource will be assigned at the max unit of below 100%.

I hope this helps.

Julie