Lots of cheapish things to do...
kojaks or primo comets
Flat bar with bar ends (lower than an S bar with an M handle post)
SPD
TI seatpost
Narrow ass hatchet type saddle
58 tooth chainring
2 speed rear wheel to drop some weight
if fendered take them off.
Get stronger (actually ride a lot to get used to whatever you go with)
My brompton with a 1 speed wheel and 58 and 38 chain rings is maybe 1 mph slower than my 82 700 c Holdsworth with wide gearing over 20 miles or so. Where it is a lot slower seems to be climbing. With kojaks and stripped down a few lbs it would be closer to the 700 c bike.