You can run certain skimmers externally. AquaC EV series, the skimmer that i own, can be run outside of a sump, but only skimmers for large tanks can usually handle this. the most efficient way, not the only, but the best is to have a large water pump, mag series are common, and this would feed the skimmer. Now skimmers run this way, need to have a lot of air to water volume, so there usually large, or specially designed for this set up. high end deltecs are designed to be run externally.
As you asked the question and i gave an answer, i will no give my advise. I would strongly advise against this setup, as you will spend a lot of money, for something that is just not wroth it. A simple aquac hob series skimmers, and even coralife skimmers would work just fine, and not cost an arm and a leg. On the flip side you can run the skimmer for a larger tank, that is within the skimmers operation range.
A lot said, sorry for the long response.
