You can offer act of charity in its place. An extra offering in the poor box, praying for others, doing something for others, etc. all done with the intention of substituting it for the fasting from meat. It is an excercise done to forget about yourself out Love for God. And doing those other things can help do that for you too.
The following is from the U.S. Bishops (USCCB)
Voluntary fasting from food creates in us a greater openness to God’s Spirit and deepens our compassion for those who are forced to go without food. The discomfort brought about by fasting unites us to the sufferings of Christ. Fasting should bring to mind the sufferings of all those for whom Christ suffered. One may refrain from certain foods strictly for dietary purposes, but this would not be Christian penance. Rather, our fasting and refraining is in response to the workings of the Holy Spirit. By fasting we sense a deeper hunger and thirst for God. In a paradoxical way, we feast through fastingâ€”we feast on the spiritual values that lead to works of charity and service. Did not the prophet Isaiah proclaim that such works characterize the fasting that God desires?
This . . . is the fasting that I wish:
releasing those bound unjustly,
untying the thongs of the yoke;
Setting free the oppressed,
breaking every yoke;
Sharing your bread with the hungry,
sheltering the oppressed and the homeless;
Clothing the naked when you see them,
and not turning your back on your own. (Is 58:6-7)