From an Operating System standpoint, the two SSDs will use different partitions. There is no way to span a single file across multiple partitions that I know of. I think that the only way you could do that is to build a RAID 0 array with the two SSDs and partition that as a single 240GB partition. That should give you sufficient space to hold the file. Of course this really depends on exactly how much space is really available on your SSDs, you need to take OP into consideration as well.