Spawning L4D1 Survivors in L4D2

Pros:

It works perfectly fine, and it's awesome!!!

Cons:

They tend not to follow, but have to kick them and re-sprawn them in order for it to take effect, the bots (l4d1) won't follow can't be resolved for now, but the only tentative way is to kick them then re-sprawn them.

Conclusion:

Though "exec l4d1sur" worked in my l4d2 game, but in order to fix issues on spawning Bill, here's the solution as below here is what I EXACTLY did, and it seriously works, bet this is the only solution to many who experienced why these additional bots won't follow and remained in the safehouse.

[Step 1]: I went to the console and typed sv_cheats 1 command.

[Step 2]: Below here, this is what I typed
prop_physics_create survivors\survivor_teenangst.mdl
prop_physics_create survivors\survivor_manager.mdl
prop_physics_create survivors\survivor_biker.mdl
prop_physics_create survivors\survivor_namvet.mdl


[Step 3]: Modifying the survivor behaviour so they can actually move
sb_l4d1_survivor_behavior 0

[Step 4]: Then finally I spawn them (including Bill, and so far I experience no glitches, Bill do appear, but same problem as the rest, they don't follow!)
sb_add louis
sb_add zoey
sb_add francis
sb_add bill

[Step 5]: Remove them, cause the reason is the first spawn, you all know they won't follow, but...
kick louis
kick zoey
kick francis
kick bill

[Step 6]: By re-spawning them again (as of step 4), you will see them acting as bot players.
sb_add louis
sb_add zoey
sb_add francis
sb_add bill

[Step 7]: Once you finished the game e.g. c1m1_Hotel, (as in reached the checkpoint) and got into another map like e.g. c1m1_Street, repeat Step 1 to Step 6 again.