Hi Martin,
I'm working with Sparx on this. [Actually something similar, but it might lead to what you want as well.]
I believe it can be done, but I have not worked out all the steps in detail.
As an example, take a look at the library provided by Sparx.
HTH, David
BTW: There appears to be no way to transfer these between projects. You could - given a solution to your stated need - distribute the library, but you could not export the images from one project and import them into another. This is another area that needs to be addressed.
Perhaps you'd like to start a feature request thread on either or both of these. Here's our (local) best practice.
Start by creating a new thread. You can use this one since it is already here, or (in future) create a new one in the Suggestions and Requests section of the forum. This way there is someplace for us - the user community as well as Sparx to discuss the issue, refine the requirement, post workarounds, and generally keep up on what's happening.
Then submit a feature request directly to Sparx. This actually gets the request into their 'hopper.' [This is a user forum, though Sparx is very active here too.] You can reach the correct form by clicking the Feature Request link under the Support link at the bottom of any forum page. [There is also another feature request link at the bottom of the Registered Users main Web page.]
In your feature request please quote the title of the associated forum thread, and paste in the URL. This will let Sparx participate in any discussion. They can often solve the problem, or provide helpful advice in the meantime.
Finally, if you hear back from Sparx please post back to your thread to let us know what they have to say.
David