No, this is not possible with any supported API's. Also, please don't. Topmost and similar things are reviled by users and run afoul of the "What if two programs did this?" principle.

Historical windows were ordered based on their Z-Index, and the Z-Index could be held above other windows with the Topmost style. Windows 8 added a new layering system called bands, which are not exposed to developers and require the caller of the API's to be cryptographically signed by Microsoft. These layers exist on-top of the desktop windows (which is where Z-Index lies). The topmost band is ZBID_UIACCESS since it represents soft-input panels that are meant to be the user's means of controlling other applications.

ADeltaX has a great summary on his blog of what has been reverse engineered about the bands system.

(Yes, ZBID_UIACCESS is accessible with signing and uiAccess="true" manifest, but that's still not supported for non-assistive technologies)

Related: Is it possible through the Windows API to place a window on top of jump list windows?