Thanks for the trick with photoshop-->pdf placement, I will have to give that a try sometime in the next week or so, but my ultimate goal is to use only FOSS software.
Is free solution which works similarly. Needed 3 programs: Scribus, Notepad++, Ghostscript
1. place in Scribus Your photo
2. publish it file as pdf in greyscale mode
3. open your pdf file in notepad++
4 replace 7 0 obj
<< >>
endobj and paste
7 0 obj
[/Separation/PANTONE#203295#20C/DeviceCMYK<</C0[0.0 0.0 0.0 0.0]/C1[1.0 0.0 0.529999 0.210007]/Domain[0 1]/FunctionType 2/N 1.0/Range[0.0 1.0 0.0 1.0 0.0 1.0 0.0 1.0]>>]
*explanation C1 shows cmyk values to display for example C1[1.0 0.05 0.5 0.0] it is C=100 M=5 Y=50 K=0
PANTONE#203295#20C = PANTONE 3295 C
5. add in 10 0 obj
/ColorSpace 7 0 R
/Decode[1.0 0.0]
/ColorSpace /DeviceGray -
deleteYou should have
10 0 obj
<<
/Type /XObject
/Subtype /Image
/Width 472
/Height 544
/BitsPerComponent 8
/Length 11 0 R
/Filter /DCTDecode
/ColorSpace 7 0 R
/Decode[1.0 0.0]
>>
endobj
6. save file
7. convert your pdf in pdf in ghostscript (cleans the file = Repair XREF table, in new pdf there are more characters)
Sometimes You can try pdftk and in terminal paste pdftk broken.pdf output fixed.pdf
After this way You have pdf file similar as from photoshop.
I attach sample file.