I got some blobs called 'sticki dots' or something like that. They fit into the boon nicley and stick better than bluetack with a lick of the thumb. Thats not to say that its great, just better.
Double sided sticky tape seems to work nicely if you just stuff the hole with the stuff (pun intended) although the stuff mentioned above should work just as well.
Try Hobbycraft, they do glue dots which are blobs of golden coloured glue stuff about the size of a Rice Krispie and they stick to flesh etc very well.
I've had success with a tacky bee's wax substance used for holding candles in place. I usually find cards with a dozen or so dots for under a dollar at craft shops.
DF Tape can be used but you want to "soften" how sticky the active side is & the side you will use) so it's easier to get on and off.
Though I love this style of writer I ultimately became so fed up with this very issue that I simply went to using my Banjo Pick or TT styled swamis