You can mount the 2nd drive in a folder on the first one. You don't really want RAID-0 because if one drive dies, all your data is gone. You don't want JBOD because...well JBOD is garbage. Windows can't boot from a dynamic disk anyway, so you can't use the built in Windows utility for it.
To mount a drive in a folder instead of as a drive letter you can
Right click on My Computer and select Manage. Then click Disk Management Select the volume you wish to mount inside of another and click Change Drive Letter and Paths From there you choose Mount in the following empty NTFS folder
This will hide the second drive letter and it will look like a normal folder on C: or wherever else you choose to mount it.