Probably the easiest way to accomplish this would be to utilize a LV 2 style global. This is a while loop with a case structure. The case structure can have two cases a read and a write. The write case will place values into an unitialize shift register and the read case will read from the shift register. The outer while will have a constant wired to the conditional to only allow 1 iteration of the while loop. This is a combination of an action engine and a LV2style global. Place the subvi in both vi's and call the read and write actions. This is an easy way to share the data between both processes. If you only have 1 subvi open at a time it is probably easiest to place all the subvi's embedded. If you want them to run and allow the top level vi to continue to run load them dynamically using vi server. Hope this helps.
