How to pass the actual coordinates in MDI_COMMAND

Hi!
I want to create button (pyvcp or hard external - no difference) to set the offset G54-G59 commands.
In ini file in {HALUI} section there are several strings:
MDI_COMMAND = G10L2P2X[$XVALUE]Z[$ZVALUE]
MDI_COMMAND = G10L2P3X[$XVALUE]Z[$ZVALUE]
where XVALUE and ZVALUE - actual X,Z coordinates.
How can I transfer the actual coordinates to halui.mdi-command-XX?
The operator set the tool near desired point and push "G54 button"
The offset of new coordinate system will enter in EMC.
Is it possible?
Or I need to change the halui.mdi-command-XX on the fly?
I know the actual X and Z coordinates (axis.N.motor-position-cmd).

Hi!
Thank you!
It works.
G10L20 the same I need.

can i use this to have an offset button. i want to be able to
touch my material(/w edge finder) and then click pyvcp button
to offset it to half. so far i have this. is there another pin i need to 3
be connected to ? T'anks !

postgui.hal
net mdi-offset halui.mdi-command-04 == pyvcp.mdi-offset

axis.ini
MDI_COMMAND = G10L2P2 X.125 y.125