Might be a bit late but here is more formal solution

This is documented here

https://learn.microsoft.com/en-us/azure/cosmos-db/analytical-store-introduction#representation-challenges-workarounds

SELECT CAST (num as float) as num
FROM OPENROWSET( 
       PROVIDER = 'CosmosDB',
       CONNECTION = 'Account=<account-name>;Database=<database-name>;Region=<region-name>',
       OBJECT = '<container-name>',
       [ CREDENTIAL | SERVER_CREDENTIAL ] = '<credential-name>'
) 
WITH (num varchar(100)) AS [IntToFloat]