No can do.
The ginput function suspends all interactive properties of a figure window so even if a WindowsButtonMotionFcn function were written to continuously update the position of a text object to follow the cursor, the ginput function will temporarily disable it while in use.
You could, however, include the text instructions in a stationary position.
Example:
% Create demo figure
fig = clf();
ax = axes(fig);
% Place text in upper, right corner of axes.
tx = text(max(xlim(ax)), max(ylim(ax)), 'Select point 1', ...
'HorizontalAlignment', 'right', 'VerticalAlignment', 'Top', ...
'Color', [0 0 .80, .5], 'BackGroundColor', [.27 .51 .70, .5], ...
'FontSize', 14, 'FontWeight', 'Bold');
% Get point 1
[x(1),y(1)] = ginput(1);
% Update text
tx.String = 'Select point 2';
% Get point 2
[x(2),y(2)] = ginput(1);
% Remove text
delete(tx)
