In Acrobat there's a fixup "Map specified process color into spot color "Light Brown"
I think you can modify that one to achieve what you want...
Here is a more detailed instruction if you have not created the fixup already. The "Light brown" fixup si acctually for turning Pantone colors into CMYK, and you asked for the other way around.
The easiest way is to create a new Fixup. Follow this guide with the attached screen shots:
1. Click on the Tool button for Preflight fixes.
2. Click on the Options up in the right corner and choose Create new fixup.
3. Give a good name to the fix, up in the left corner.
4. Write the word Map in the search (Find) window up in the right corner and Click on Fix called “Map colours”.
5. Define the mapping you need starting with the CMYK you will convert.
6. Check the box for “Creaste as Spot color” and write the Pantone name you will have.
7. Click OK.
8. From the Option menu – choose Export Preflight Fixup.
9. Import the Preflight profile in FF Core.
Remember to write the name exactly as you would find it in the Pantone library in InDesign or on your DFE.
You can also use this kind of fixup to convert to RGB or Grey. Just change the “Destination color model”
The fixup “Map spot and process colors” will start with the Pantone name and it can convert to CMYK or just map it to a different pantone name.