Query/Table Hints for the History Table when Using the FOR SYSTEM_TIME Clause
While not a great idea in general, a workaround that seems to work is using the USE PLAN hint

Base query to get the XML from

-- UNION ALL instead of FOR SYSTEM_TIME clause - Table Hints
SELECT  *
FROM    dbo.People WITH (INDEX(IX_Live_People__Name))
WHERE   LEFT(VolatileData, 2) = '2A'
    AND Name = 'John'

UNION ALL

SELECT  *
FROM    hist.People WITH (INDEX (IX_Hist_People__Name))
WHERE   LEFT(VolatileData, 2) = '2A'
    AND Name = 'John'


Get the XML


Replace ' with ''



Run the query with USE PLAN and the previously generated execution plan

SELECT  *
FROM    dbo.People  FOR SYSTEM_TIME ALL 
WHERE   LEFT(VolatileData, 2) = '2A'
    AND Name = 'John' 
OPTION(USE PLAN N'...')


Result





Using a plan guide to force the plan

Change ' to '''' in the query plan from the base query



Create the plan guide

EXEC sp_create_plan_guide   
    @name = N'TemplateGuide1',  
    @stmt = N'SELECT    *
FROM    dbo.People  FOR SYSTEM_TIME ALL 
WHERE   LEFT(VolatileData, 2) = ''2A''
    AND Name = ''John''',  
    @type = N'SQL',  
    @module_or_batch = NULL,  
    @hints = N'OPTION(USE PLAN N''Plan Here'')'


Test the query

SELECT  *
FROM    dbo.People  FOR SYSTEM_TIME ALL 
WHERE   LEFT(VolatileData, 2) = '2A'
    AND Name = 'John'


Result



The plan guide is used, based on the PlanGuideName fragment in the plan's XML

PlanGuideName="TemplateGuide1" 


&amp;

UsePlan="true"




As expected, when we add a couple of spaces the plan guide is no longer used

SELECT  *
FROM      dbo.People  FOR SYSTEM_TIME ALL 
WHERE   LEFT(VolatileData, 2) = '2A'
    AND Name = 'John'   


Resulting in the query without the index hints



(Tested on build version 14.0.3045.24 / SQL Server 2017 CU12)



Notes

While this is a possible workaround it is only meant to be used if it is A) needed and B) there are no other options.

The use of plan guides is most beneficial when using  paramaterized queries (either by design or force), creating a plan guide for each ad hoc query possibility is not feasible.