Is it possible to link a secondary Windows machine to my main machine over a network so they can mine the same block?
Everyone is mining on the same block at the same time. So just point each miner at a pool, that's all you need to do.
Hmm, not strictly true as each pool is constructing its own new blocks to mine on. In fact several. simultaneously, so if you have more than one worker, they may be mining different blocks. But as soon as a block is solved, that gets broadcast to the net and all of the pools (and solo miners) drop their current blocks and start again using the newly mined block as a basis.
As a further twist, AFAIK a stratum protocol miner actually assembles the final block header locally. So you could say that
all (stratum) miners are working on different blocks.