Most (maybe all?) 2.5D milling packages will do what you are looking for - even though a helical plunge is technically a 3D move. A 2.5D program will usually be programmed from something like a DXF (stick drawing) and will not calculate toolpaths from surfaces.
You should be getting a demo to evaluate from your vender or at the very least a guided "tour" of the software with a Q & A session. These will answer your questions.
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