This is the best I can think of:
th = text(-10.05,0.94,'Hello WORLD!'); % Some text-coordinate in a figure of mine
txt_size = get(th,'Extent'); % gives [x0 y0 dx dy] of text-in-axis
txt_end = -9.975; % "Desired" end
while txt_size(1) + txt_size(3) < txt_end
set(th,'fontsize',get(th,'fontsize')+1); % increase fontsize by 1
txt_size = get(th,'Extent'); % get the text extent
drawnow % for dramatic animation!
end
HTH
