rubeus has developed a more advanced version that you can download here. Please download his version unless you're using an older Sigil version and/or Python 2.7.x.
With the help of
KevinH, who gave me some extremely helpful pointers, I've created a very simple proof-of-concept plugin that duplicates the functionality of
Tools > Add Cover but doesn't touch the existing cover or the guide section.
Usage:
1. Install the plugin as usual.
2. Select Plugins > Edit > SVGWrapper > Start.
3. Click the arrow of the dropdown box, select an image and click Insert.
4. Repeat step 3 until you've added all the desired images.
5. Click Done to close the Insert Image dialog box and OK to close the Plugin Runner dialog box.
Known issues:
1. The Book Browser won't be updated if you click the Insert button, but the plugin will write a
xxx.xhtml added message to the Plugin Runner window. (The Book Browser will be updated when you click Done.)
2. You can't select the location or the name of added images. (Each image will be added at the beginning of the book using the image name as the file name.)
Credits:
This plugin uses code originally developed by the
KindleUnpack developers.