The thing that you need to do is create a "dead key" state. You can create one in Ukelele with the "Create" button in the tool bar.
You might be interested in a lightly custom layout that I created by applying the results of a paper I found online that suggested the creation of a new greek keyboard layout (called ΝΕΠ) and the Dvorak layout.
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| ' | , | . | π | υ | φ | γ | δ | ρ | λ |
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| α | ο | ε | ς | ι | ΄ | η | τ | ν | σ |
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| ; | ψ | ξ | κ | χ | β | μ | θ | ω | ζ |
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