Yes. Use LVM.
Using Logical Volume Manager, your volumes can span multiple partitions on multiple devices. You can expand a logical volume by adding a new device to it, then grow your file system into the new space. Your file system will be one contiguous space across multiple devices.
First, setup your initial storage space using LVM. A single volume group and volume should do the job. Then when you need to example it, add a new EBS volume, attatch it to your instance, add it to the volume group, grow your file system into the space, and viola: more space with no downtime.
Later, consider creating a new device as a larger single EBS volume (again with LVM!), synchronize your data to it, and rotate your services to it. This can be done with a minimum of downtime since it can be prepared on the side and will let you snapshot your volume as one EBS device again. Otherwise the snapshot mechanism of AWS becomes kind of useless unless you freeze or unmount the file system before you snapshot.