You could cut right through, but leave a few small & thin holding tabs to keep the part in place.

The next stage would be to generate a toolpath that cuts away those tabs, but before running the code, apply some hot-melt glue in the already cut areas to provide support whilst the tabs are cut.

So similar to you own idea except no need to grind the the other side to release the part.

Martin.

As you are using Fusion that has the facility to add "tabs" to the contour cut, when setting up the contour geometry there is a box to click if you want tabs and that then allows you to enter length, thickness and positions.

Tool will lift and drop as it goes around the work. Simply file off the thin tab when cleaning up the edges.

Some people apply good quality painters tape (blue 3M) to a sacrificial surface and then use superglue to hold the stock to that which can be peeled off after cutting but you need to be careful with thin items that you don't bend them.

Elsewhere on here I've described applying blue masking tape on surface of a backing plate and on the underside of the material; then gluing the latter down with superglue. Relatively easy to peel the blue tape off.

Another approach which should work is just to superglue it direct – this is more secure but harder to remove. However I once by mistake forgot to apply the blue tape to the material so had to remove it with heat – I found that a relatively short boil in water did an excellent job. As people use superglue as a replacement for "wax chucks" (see Clickspring videos) it's only the same idea applied to milling.