It is clear to me that the Europa method of fixing the cowlings with anchor nuts and screws is a non-starter. Some kind of quick release is an absolute must. Looking at sites like Aircraft Spruce shows you can get receptacles, grommets, retainers etc in all sorts of shapes and sizes. The possible combinations are astronomical and and how do I know any of them are suitable for the Europa?
Raimo Toivio advises Milspec fasteners. Turns out they have a one-size-fits-all adjustable solution.Two in fact. At their recommendation I opt for the larger 4000 series, though seeing how solid they are (these can hold an Apache together!), the 2000 series would probably have done fine. They're also slightly cheaper. The photo shows the parts and tools you get from Milspec.