Pre-paying import duty?

I recently came back from a trip around Italy, and whilst there sampled some fantastic liqueurs. I couldn't buy anything more than a taster bottle as space/luggage weight was incredibly tight.

I want to order some now that I'm back in the UK, and I know that I have to pay import duty and VAT on it. The seller doesn't operate a duty-paid system - is there any way I can pre-pay the duty/VAT in order that DPD/Parcel Force/whoever don't charge me a fee for calculating and paying these taxes on my behalf?