Writing transparent rasters to Adobe Geospatial PDF

Here's my use case: I create a map in FME with a basemap, lines and points. Some of my points I wish to display using PNG markers. The PNGs have a transparency layer. The PDF Writer (or is it the PDF Page Formatter?) does not support the transparency, and will force the transparent parts to a background colour (e.g. black).

Half-functioning work around: I can use the MapnikRasterizer to ingest my basemap, lines and points (which will correctly apply the transparency on the PNG icons), and send this raster to the PDFPageFormatter. However, since I want my lines to be drawn under the icons, the lines also need to be rasterized, so we lose the chance to output the lines as vectors within the output PDF.

I read 2 images from different WMS with an ImageFetcher. One of them is a transparent png that should be placed over the other image.

That's exactly why I need this functionality.

I also want to read WMS images from different services and write them to a pdf. The WMS reader supports transparent background, but the pdf writer does not honor that. This would enable me to automate the generation of pdf maps - something I expected I would be able to do with FME.

I was able to solve the problem with the transparent image from the WMS with RasterMosaicker, see attachment.