Call a local sign shop. Ask for a piece of Coroplast that is scratched and unsellable. If they try and charge you more than 15 bucks look for another one.
Coroplast is basically plastic cardboard. If you have ever seen a Real estate or Polical sign up close you know what I mean. Coroplast has a series of hollow tube flutes 1/8" that run the length of the material. Block off one end of the coroplast with Duct tape. Grab a shop-vac with the wide pickup nozzle and using a copious amount of duct tape and cardboard seal the other end onto the shop-vac nozzle.
Use your CNC machine to pop a couple hundred holes into the Coroplast tubes for the vac.
You now have independently suctioned tubes. You can block off sections with tape when not in use. Make sure you allow enough air into the shop-vac to not stress out the motor - you can always block off holes again. Block only as many holes as needed to give you hold down. On the plus side you also get dust collection
If the coroplast does not have a smooth enough surface for the type of work you want to do ask the signshop for AlumaCore. It is the same thing as coroplast except that it is skinned with .020 aluminum on the face and back and the tubes are about 1/4" thick. Absolutely smooth. About double / triple the cost of corpolast though.
The coroplast is cheaper but IMO go for AlumaCore if you can get it. If you cannot find either locally I can give you a list of suppliers.
Let me know the type of materials you mill - I have several specialty bases that I built to switch out in seconds on my work system. If you need a sketch, gimme a shout.