I have not tried it, but this should work: Define a pseudo asset like "EURUSD_VOL", and import a price curve of that asset in .bar format. The tick volume can then be either the High, Low, Open, or Close of that curve and you can read it with the price functions.

Alternatively you can also import .t1 format. It contains only a single data value instead of 4 and thus uses less memory. Read it with priceClose().