If you can;t leave them, you could try any of these:
wooden (not metal, generally) sealed boxes, like cigar boxes, to place the offering in so it;s able to be left a few hours
find an outdoors space, dedicate it to that spirit temp or permanently, bury the offerings there (avoid anything fatty or very sugary, chocolate, or with raisins, currants, or sultanas in, because these are toxic to a lot of animals)
use offerings like mini liqueurs that you open but then re-close and pour onto the ground or down the sink (no lavatory) afterwards.
There is a de-linking method shown in this post for making wsure, when you take an offering off the altar, the spirit’s energy is no longer connected: Tutorial : Tool-Free Magick Using Your Hands
Or finally simply don;t offer food, offer artwork, poetry, candles, incense, and leave the consumables off the list. All pisirits have a range of different things they enjoy, for example Lilith enjoys perfume, others will enjoy art or poems dedicated to them (and possibly shared on the internet, including here) and so on.
I did some artwork as offerings and that was well-received by the spirits.
If you don’t consider yourself artsy (and are not interested in developing that), think what else you could do for them, for example posting details of rituals you used and praising them when you get a result, most spirits want to spread their name and be thanked publicly.