Have a look at this thread on IAP, the guy used 25psi and it still flooded the tubes. If you can fill the tubes with blu-tac or similar then you cut down the amount of air in the tubes, just leave space at the ends of the tubes for the plugs to fit.
Whatever you use in the mix or on the tubes, make sure it is completely dry. You could try dried seeds, I have used chilli pepper seeds and fennel seeds, by using CA on the tubes and rolling the tubes in the seeds. Look forward to seeing what you make.
Peter