Sheet film developing

Hello,

I've just started developing my first 4x5's in a Jobo 2523 tank that
suits a single spiral both of which I inherited from a previous owner
of my CPE2 machine.
Since large format photography requires more set up time and
concentration I am often finding myself in a position when I need to
develop one or two sheets of film only.
At the moment, I am mostly shooting positives and do not like the
idea of throwing away 270ml of the chemistry (minimum filling value
recommended by Jobo for this tank) each time I need to develop a
single sheet. I've been thinking to break the rule and try to fill the
tank with a smaller amount of solution at the time when I load a
couple of film sheets close to the tank's outer side but I am affraid
that I do not have much knowledge of either what amount would be
satisfactory or if this is a right thing to do at all.
Hope somebody would give me an advise or redirect to some Internet
sources that would help.

Thanks,

Serge