Klick Fix and Ortlieb both offer an extension piece to add to their handlebar bag mount,
for trekking bar bikes, or other purposes..

SJS, in UK has a 1pc T and 1 bolt, like clamp, that is thinner stack than using an actual stem.

( i used a 2nd stem and 1" Tube to mount a KF bar bag mount, NB,
KF mount takes Ortlieb bags on them,
(the reverse Combo, DNF)

the bike has a suspension fork, but a rather short travel.. I have a Fork crown mount light
same position as yours, it's OK under the HB Bag,