Otherwise depending on your bicycling attire, any normal concealment method could work. For me & everyone I ride with, we wear regular lycra cycling shorts and polyester cycling jerseys with rear pockets. You can fit just about anything in a jersey pocket including a full frame auto and a holster. But a poly/stainless compact auto would be an easy fit in a jersey pocket.
I still think a belly band riding high under the jersey is probably the best concealment method on a bicycle.
Bear in mind when you talk to cyclists (such as me), it is often assumed we are talking about normal cycling clothing (lycra shorts, bicycling jerseys). If by "riding a bicycle" you mean hop on a cruiser in your street clothes and just tool around the block or down to the mail box, well that's a whole different matter.