If the hole in the PDMS is smaller than the OD of the PEEK tubing it will form a
conformal seal that is adequate for low pressures.

You might try a UV curable adhesive.  I've had good luck on polymers with
Norland Optical Adhesive from Thorlabs.

Nanoports from Upchurch would give you more surface area and a bit of strain
relief.  They can be used with the optical adhesive as well.

--
Jack Rundel
Department of Chemistry
Oregon State University