I too was guilty of buying in advance of having space in the garden but because I had nowhere to put the plants I had nowhere to heel them in
When I purchased in the Spring I repotted them all in the same soil they eventually would be buried in, usually in bigger pots. These would sit in the equivalent of a child's wading pool for months sometimes; I actually used $5 air mattress seconds - their valves didn't work
- cut in to top and bottom, and used like two pool liners to hold a couple of inches of water. If some still had not found a home in a flower bed I would heel them in my potting area with left over dirt/compost/peat moss hilled up around the pots. Clearly none of my plant choices minded sitting in a little water
but that should be considered before trying this.