Have uniformed, city-checked volunteers with some card reading machines that stand around the beggars to take in the digital payments. With prewritten sums of $1, $5, $10 on tablets that you would choose quickly. Then those volunteers would go out and raise cash from ATMs every hour or so and give it to the homeless. Or buy them groceries. Evenly spread between those in the vicinity if there are more.
After they get a considerable sum, for instance, half of a minimum daily wage per person, the volunteers would move on to a different area.
Or, just have these tablet stations across the city, unmanned, so that people can just quickly donate the money when they are waiting for the lights at a crosswalk, standing at the bus stations, near the pedestrian entrances to car park garages...
The tablets would be showing photos of the beggars' struggles or have messages to incite donations.
Then, the money would go into the system and the homeless would get equal cash payouts at designated checkpoints at the start or the end of a day.
One could also implement checks for sobriety at such places so that the homeless who are sober on pick up would get more money and be incentivized to remain alcohol or drug-free.