Simple...should we have IFA? I have no clue how we'll do it yet since IFA wasn't common back around the early 90s (from what I remember), but we could just create fictitious players for now and then follow something more realistic in later years. Such as actually creating Ichiro when we hit the season where he joined MLB, and so on.
I do want to clarify, these guys won't be a bunch of superstars and the majority of them will probably be older. It could be a veteran from Japan or Cuba with decent enough ratings to play at the MLB level, or it could be a Dominican kid that's undeveloped but has a high ceiling.
One thing to be aware of, this is definitely going to affect finances in the league but that is already something that we will have to continually tweak over the next several seasons. The economy of baseball grew exponentially between 1990 and 2010. Cash caps will likely be raised every season to try to keep a pace that can be somewhat realistic without getting out of hand. Payrolls have already been growing, as well as revenues. We just need to find a way to have everything else grow with it. As it sits right now, we'd just have a few different people bid their entire $20mil of cash in posting because it's likely that they'd replenish it quickly and how do we even decide a winning bid in that case?