Not that I've seen...
I'm thinking the only way to get the memory usage down is to decrease the number of blocks... or use compression... either way it's hard because the blockchain needs to be from #0 to current... I'm really thinking a new genesis block like compression where all current balances get fed into block #0... call me crazy...
I think you could be able to unload spent inputs, and only load in unspent. Also you could even only load in the last 100 days of unspent or something. Would require more disk reads and more CPU usage, but could save memory. Anyway just a thought right now, till I can dig into it more.
Right... the blockchain .dat will still be required to be full... memory can be used for -1000 blocks but would have to be tied to the network total block count. That would fix all the memory issues... but you'd need something more than a R-Pi though I'd think to handle any read calls on the blockchain file such as a sync to another wallet.