Probably you found the solution or workaround by yourself, but I had the same problem and I found this question on Google, so I'll write an answer for future developers.
It seems that enabling delete on termination cannot be done during creating or attaching an EBS, but only via modify instance attribute operation.
This answer explains how to do this via CLI.
Analogous method for AWS SDK for Java is to change device mapping settings by using AmazonEC2Client#modifyInstanceAttribute()
My code looks like this:
EbsInstanceBlockDeviceSpecification ebsSpecification = new EbsInstanceBlockDeviceSpecification()
.withDeleteOnTermination(true);
InstanceBlockDeviceMappingSpecification mappingSpecification = new InstanceBlockDeviceMappingSpecification()
.withDeviceName(deviceName)
.withEbs(ebsSpecification);
ModifyInstanceAttributeRequest request = new ModifyInstanceAttributeRequest()
.withInstanceId(instanceId)
.withBlockDeviceMappings(mappingSpecification);
ec2Client.modifyInstanceAttribute(request);