In 2009, used Waiohai for KoOlina (II request) and then used an AC (from Waiohai deposit) to add another October week at KoOlina (three bedroom ocean view) during flexchange.
For 2010, we used Mountainside studio for Oct. Kauai Lagoons 2 bedroom oceanfront. (about a month before flexchange, but request only took a few weeks even though we only requested one date to match up with our previously booked Waiohai week) (using one bedroom Mountainside for II request exchange to Waiohai).
In 2011 we used an AC (one of the good ones for depositing Waiohai, not sure they have the no grid anymore) for a September 20ll Maui Ocean Club 2 bedroom during flexchange. (a very late deposit...one week until check in)
So it has been possible, however it seems weeks in general, and during Flexchange are showing much later (as the DC evolves) than before, so that there is much less lead time to be able to use them.
I have been following the Spanish Marriotts this year. With an AC, they rarely show up at all, and then usually only studio. Even as Getaways, they were still listing one on check in day, and it still did not show up at all with the same type grid AC we used last year for a three bedroom ocean front at Playa Andaluza, (one month before) and a two bedroom at Marbella. Taking into account the week before and after Easter, there still is much less available now. Since the Spanish resorts are not a part of the DC, one can only assume that DC may be raiding the II inventory to supply DC requests through DC II. (Although, to be honest, I was able to use Shell points for Playa and Son Antem in late March, but have not seen much except Nov. and availability showing up very close to check in since then.)
However, I still think if you are flexible (about Hawaii resorts and dates) you have a good chance of getting an exchange request filled. We do have a request in now using our Waiohai week for Maui Ocean Club. However, we are asking for only one date, to match up with our previously booked week, so we may be in for a late match if they match it at all. It was requested last year for an October 2012 check in, so I am not worried yet.
Good luck!