AWS let you import your own custom virtual machine file as AMI.
There is a hint on how AWS virtual machine start the instance :
GPT partitions are not supported by Amazon EC2, which means that
imported system volumes must have an MBR to boot.
So maybe you can try build a dual boot virtual image and upload to AWS as long as you comply with the stated limit (like create MBR boot, use complied OS allowed as AMI OS). You can't simply create any virtual image and upload to AWS.(you can't create a DOS, OS2, OSX,etc, there is many reason why AWS forbid them.)
However, since there is no way to channel AMI startup screen(Though virtual environment may let you channel KVM[keyboard,video,mouse], no cloud provider want to do this because it is counter-intuitive and counter-productive), so you can't select which boot section to boot, and there is no way to pass data in the bootup screen. You must bootup the OS first and switch the boot environment and restart.
In short, AMI image is cheap(unless you create an Gigantic hundred GB AMI), it is not worth the trouble.