I backup to an nfs share "/rman" and I want to restore on another server with the backup pieces in a different directory "/may09"

I've tried

run {
allocate channel d1 device type disk format '/may09/%d_%u_%p';
restore database;
release channel d1;

But it's still looking for the backup pieces in "/rman"

I know I can restore archivelogs using
set archivelog destination to '/may09/archivelogs/MYDB';

I've scoured the manuals and can't figure out how to set the datafile backup piece source.