Different bitmap for "welcome" and "finish"?

I have one bitmap (164x314) for the "welcome" page, but want to use a different one for the "finish" page.

I've experimented, but can only set MUI_WELCOME_FINISHPAGE_BITMAP once (for both). Is there a way to set different bitmaps for the two pages?

use MUI_PAGE_CUSTOMFUNCTION_PRE to call a custom function just before displaying the welcome and/or finish page. (Write to $PLUGINSDIR\iospecial.ini)

From the docs:

In the Pre function of the Welcome page and the Finish page, you can write to the InstallOptions INI file of the page (ioSpecial.ini)