I have had a similar problem. One workaround is to create a new table (i've called it 'Dummy') with just the relevant dates, and created a calculated column in 'Dummy' with the following:
=SUMX( FILTER('Table','Table'[Date]<='Dummy'[Date]) , 'Table'[Amount] )
After this you should be able to relate 'Table' and 'Dummy' and just pull the cumulative figure from 'Dummy' as you need it.
It's not ideal, and if anyone has a neat formula for obtaining this result without resorting to the creation of an extra table shout.