It's simple enough.

Firsstrike gets its linking information from the names of the control points.

Link format:
<Control Point name>_pushmap_<CP number>__<CP link number>

<Control Point name> = name of the Control Point.
pushmap = keyword to let Firststrike know that the numbers that follow are to be used for linking.
<CP number> = number of this control point.  This number is chosen by the mapper to identify this CP.
<CP link number> = the CP number that you want this CP to link to.  You can link to as many CPs as you wish.  Just separate each by a single underscore.
*Note that you must separate the <CP number> and <CP link number> with double underscores.

For example...

You have four control points.  A, B, C, and D.  You want A to link to B and C.  You want B and C to link to D.  You would name your CPs as follows:
A_pushmap_1__2_3
B_pushmap_2__4
C_pushmap_3__4
D_pushmap_4

Say you want CP D to link to B and C?  Simple adjustment:
A_pushmap_1__2_3
B_pushmap_2__4
C_pushmap_3__4
D_pushmap_4__2_3

You now have linked CPs!