I assume you mean that the outbound is currently available (it is within 355 days) but your inbound is more than 355 days out and currently cannot be booked. You book the outbound with the 241 now either online or by calling. When the inbound becomes available at 355 days you call and add it to the 241. There is no fee to add an inbound that was not available because of the 355 day booking restriction.
See the threads linked in this post:
http://www.flyertalk.com/forum/26828153-post2.html
You do not want to cancel your outbound flights and rebook as there is no guarantee that they will be returned to award inventory.
You cannot combine the AMS-LHR redemptions with the 241 redemptions. Those will be booked as separate tickets.