You cannot make spreader setups lossless (with the exception of something like a pulse activating a block that doesn't consume mana, e.g. a drum or hourglass), so your only real option is to make the burst as small as possible. Messenger and velocity lens both reduce burst size somewhat reasonably, messenger way more than velocity. Using both together yields the smallest possible burst size, but you will need to apply the weight effect via a mana prism.
Your other option is to just break the blocks in any other way and smelt them. Or use them in-place, if you want to make livingrock.