No - the only solution is to have a products set up which sells for 1p per item and then sell multiples of that item.
Or if something sells for 50p per gram have the product sell for 50p and then if someone buys 100g you sell 100 items of that products @50p each.
It's a very untidy and inelegant solution which really makes a mess of reports. I would have thought it would be pretty easy to solve.
Thankfully we don't sell weighed items any more but this doesn't help anyone who does....